Fire in the East

XIV

The stricken plain beyond the western wall of Arete was a ghastly sight.

From the roof of the gatehouse there was a panoramic view of the horror. Like flotsam thrown up on the shore after the storm has spent its fury, the Sassanid dead lay in distinct waves across the plain. The furthest wave was some 400 to 200 paces from the wall. Here the dead lay as individuals; crushed by a stone, skewered by a bolt, grotesquely half sunken in the ground in the trap which had killed them. The next wave ran almost to the wall. Here the dead at least had company, lots of company. They lay in lines, groups, even low hillocks. Here they had found another way of dying. The often brightly dyed feathers of arrows fluttered in the fresh southerly breeze. Bright, gay, like bunting at a festival, they added an inappropriate, macabre touch to the scene of devastation. Finally, there was the horror below the wall. Piled on top of each other, three, four, five high, they concealed the earth. Smashed, twisted and broken, the corpses here were almost all burnt.

For eighteen years, more than half his life, Ballista had had a particular horror of being burnt alive. Since the siege of Aquileia, everywhere he had served he had seen men die in flames. The High Atlas Mountains, the green meadows of Hibernia, the plains of Novae by the Danube, all had brought forth their crop of the burnt ones and here they were again at the foot of the wall of Arete; hundreds, possibly thousands of Sassanids burnt by naptha and white-hot sand, their thick black hair and tightly curled beards reduced to charred wisps, their skin, turned orange, peeling away like singed papyrus, obscene pink flesh showing raw underneath.

Although there was the continuous low buzz of innumerable flies, the bodies looked strangely uncorrupted. It had been thirteen days since the assault. On comparable bloody fields in the west, Ballista knew that after four days the corpses would have begun to rot, fall apart, become unrecognizable. Here, the corpses of the Sassanids seemed to be drying up like dead tree trunks, without putrefaction. Turpio, boasting his local knowledge, put it all down to diet and climate; the easterners ate more frugally and were anyway desiccated by the dry heat of their native lands.

The Sassanids had not gathered their dead. Possibly they thought it would be interpreted as a sign of weakness if they asked for a truce to collect them. Maybe it was just unimportant, given that they would then expose the corpses to the birds of the air and the beasts of the fields. Ballista noted that religious scruples had not held them back from looting the dead. No one could leave the city of Arete; all the locals were refugees, in the town or elsewhere or – the gods have mercy on them – prisoners of the Persians – yet every morning more of the corpses were naked; armour, clothes and boots gone. The scavengers could only come from the Sassanid camp.

Thousand upon thousand of dead Persians; it was impossible to estimate their numbers. Demetrius told how the Persian king calculated casualties. According to Herodotus, before a campaign 10,000 men would stand packed as closely as possible together. A line would be drawn around them. They would be dismissed. A fence, about navel-high, would be constructed on the line. Ten thousand men at a time, the army would be marched into the paddock until all had been counted. At the end of the campaign the procedure would be repeated, and the King of Kings could find out how many men he had lost.

Bagoas laughed a bitter laugh. He claimed to know nothing of this Herodotus, but clearly the man was a liar or a fool. What good would it do to know casualties to the nearest IO,OOO? In reality, before Shapur, the beloved of Mazda, went forth to chastise the unrighteous, he had each warrior march past and drop an arrow. When the Mazda-worshipping King of Kings returned freighted down with fame and plunder from the lands of the non-Aryans he had each warrior pick up an arrow. Those arrows remaining gave the number of the blessed who had gone to heaven.

Demetrius shot the Persian boy a vicious look.

Ballista did not press the matter. He knew that the actual number of Persian dead was unimportant. Another hundred dead, another thousand dead – in itself, it made no odds. Given their overwhelming numerical superiority, it was not the Sassanid bodycount that mattered but their willingness to fight, and Shapur's willingness to commit them to fight. Ballista knew that to save the town of Arete he had to break one or the other. He suspected that the Persians would crack before their King of Kings.

Roman casualties were by comparison negligible. Yet they were higher than Ballista had anticipated, higher than was sustainable. The Sassanid arrow storm had been like nothing the northerner had experienced before. For a time he had thought it would empty the battlements of defenders unaided. If the easterners could be brought to repeat it for three or four days in a row, the defenders would simply run out of men. But Ballista knew that no troops in the world could stand before the walls of Arete day after day and take the casualties the Sassanids had endured.

On the Roman side, the bowmen had suffered most. The six centuries of Cohors XX Palmyrenorum had suffered over 50 per cent casualties. Each century was now down to just fifty effectives. The legionaries of Legio IIII Scythica had escaped more lightly. On average, each of the eight centuries along the western wall had lost ten men, bringing their numbers down now to about sixty each. Ten of Mamurra's artillerymen were absent from the standards. Extraordinarily, as they had been in the eye of the storm, just two of Ballista's bodyguard, the equites singulares, had fallen.

Of the combined Roman casualties of well over 400, about half were dead. They had been buried in the open area to the east of the artillery magazine, which had been designated an emergency cemetery. Ballista was very aware of the dangers of plague and disaffection if the bodies of the defenders were not treated with all due respect. Issues of health and religious sensitivities made the extra effort of burial more than worth while. The rest of the casualties were too badly injured to fight. The majority would eventually die; many of them in agony from blood poisoning. Before that happened, the military medical teams would be very busy. Every trained soldier who could return to the ranks would be very necessary.

When the Sassanid assault failed they had totally quit the field. They had dragged away out of range their mantlets and ballistae, and the luckiest of their wounded. The following day they had stayed in camp, given over to their mourning; high, wild music and wailing, barbaric to western ears. Then, their grief somewhat assuaged, they had turned their hands again to the siege.

The surviving siege tower, the southernmost City Taker, the one which had fallen through the roof of an underground tomb, was hauled back to the Sassanid camp, where it was promptly broken up. The majority of its timbers were reused to construct a very large wheeled shed; what the legionaries called a 'tortoise'. Bagoas was happy to tell everyone what the shed would shelter – no less than the illustrious Khosro-Shapur, the illustrious Fame of Shapur, the mighty ram that had battered down the double walls of the city of Hatra. For fifteen years since that glorious day, Khosro-Shapur had rested, dedicated to god. Now Mazda had put it in the mind of the King of Kings to bring the great ram forth to give anew evidence of its prowess. It would have been transported in pieces, and was now being reassembled to be hung from mighty chains under that shed. Nothing, Bagoas earnestly assured his listeners, nothing, neither gate nor wall, could stand against it.

Thirteen days since the assault, and now it was all going to happen again. Ballista looked out at the squat shape of the tortoise under which sheltered the Khosro-Shapur. He wondered if he had done enough to deny it, to keep it out. Certainly he had done what he could to replace the casualties. Two troopers had been transferred into the equites singulares from the turma of Cohors XX led by Antiochus on the north wall. Likewise, ten legionaries of Legio IIII had joined Mamurra's artillerymen from the century of Lucius Fabius at the Porta Aquaria on the east wall. Ballista had noticed that one of the replacements who appeared on the battlements of the Palmyrene Gate was Castricius, the legionary who had found the body of Scribonius Mucianus. Four hundred men from the numerus of Iarhai had been ordered to take their places on the desert wall. Ballista had made further specifications: 300 of them were to be trained mercenaries and only 100 recently recruited levies; the caravan protector was to lead his men in person; Bathshiba was not to be seen on the battlements. (Ballista put away, as something to consider later, whenever there was time, the strange, new reluctance to fight on the part of Iarhai.) The new arrangements meant that the western wall was nearly as well manned as before the assault. It did, however, mean that the other walls were each defended by only 200 mercenaries backed by a small number of Roman regulars and, in the cases of the east and south, a crowd of levies. Ballista knew that, as the siege went on and casualties mounted, he would be forced to rely more and more on the local levies. It was not a reassuring thought.

Across the plain the Drafsh-i-Kavyan, the battle standard of the house of Sasan, flashed red, yellow, violet in the early morning sun as it moved towards the great battering ram. It was followed by the now so familiar figure on the white horse. As Shapur arrived the magi started the sacrifice. Ballista was relieved to see that, despite their reputation for necromancy, it involved no people. There were no Roman prisoners in sight.

Two of the defenders' ballistae had been knocked out during the assault. One had been repaired, the other replaced from the arsenal. Mamurra had done well. Three of the enemy artillery pieces had been hit; two on the approach, one during the retreat. It could be seen that they had also been replaced. But no more had been constructed. Ballista's rigorous scorched-earth policy was bearing some fruit. There was no timber for miles. If they wanted to build more siege machines the Sassanids would have to fetch the materials from a great distance. Ballista felt reasonably sanguine about artillery; he still had twenty-five pieces on the western wall to the Persians' total of twenty.

Preceded by the Drafsh-i-Kavyan snapping in the wind, Shapur rode across to a raised tribunal, where he took his seat on a throne glinting with precious metals and jewels. Behind the throne loomed the terrifying, wrinkled bulk of his ten elephants. In front were the Immortals commanded by Peroz of the Long Sword and the Jan-avasper, 'those who sacrifice themselves', led by Mariades.

Ballista found it unsurprising that Shapur had not so far tried to use his tame pretender to the Roman throne to undermine the loyalty of the defenders of Arete. Who would follow an ex-town-councillor turned brigand then traitor like Mariades? It was as unlikely as anyone trying to elevate to the purple a barbarian warrior such as Ballista himself.

The battering ram was being cleared for action, camp followers, priests and their paraphernalia herded away. A chant began: 'Khos-ro-Sha-pur, Khos-ro-Sha-pur.' Here was the heart of the matter – the great ram, the Fame of Shapur and its protecting tortoise. From where it had been reassembled, Ballista assumed that it would advance straight down the road to the Palmyrene Gate. He had based his dispositions on this assumption. He hoped that he was right. Everything he could use to frustrate the ram was at the gate. The cowhides and chaff he had requisitioned were piled near by. Would the councillors remember sniggering when their barbarian Dux had announced their requisition? Ballista's three mobile cranes were stationed behind the gate. They were fitted with iron claws, a plentiful supply of enormous rocks to hand. And then there was his new wall. For four days the legionaries had laboured to finish the wall behind the outer gate. It was a pity that the painting of the Tyche of Arete had been obscured by it. The superstitious might read something into it – but Ballista was not superstitious.

Would the King of Kings send the Khosro-Shapur straight down the road into the teeth of the carefully prepared defences? Or would he have been warned by the traitor? Since the failed attack on the granaries, there was one fewer traitor in the town of Arete. But Ballista was sure that there was at least one remaining. It had taken at least two men to burn the magazine, at least two men to murder Scribonius Mucianus and dispose of his body. Admittedly no traitor had told the Sassanids about the naptha-filled jar buried just before the gate that had trapped the central City Taker. But the northerner felt certain this was proof of a problem of communication rather than evidence that there was no traitor.

Shapur waved his arms, purple and white streamers flying. Trumpets blared and drums thundered. The great tortoise housing the Khosro-Shapur moved forward, as did the mantlets, the ballistae and innumerable hordes of bowmen.

'Do you think he practises that?' Maximus asked.

'What?' Ballista replied.

'Whirling those streamers about. Imagine what a prick he must look practising on his own. Pointless anyway. Not exactly a practical skill.'

'Why do you spend what little time you have when not rattling the bed practising those fancy moves with your gladius?'

Maximus laughed. 'It intimidates my enemies. I have seen grown men cry with terror.'

Ballista looked at his bodyguard without speaking.

'Oh, well, I see what you mean, but sure it is an entirely different thing,' Maximus blustered.

'One cannot help but think that on the whole it is a good thing that I own you, rather than the other way round.'

The great battering ram was coming straight down the road, the mantlets shielding the ballistae and bowmen flung out on either side.

Allfather, here we go again. Almost unconsciously Ballista ran through his pre-battle ritual: slide dagger out, snap it back, slide sword out, snap it back, touch the healing stone on the scabbard.

As the Sassanids came into range past the white-painted humps of rock Ballista nodded to Antigonus, who made the signal, and the artillery began to shoot. This time the northerner had instructed the ballistarii to aim exclusively at the enemy artillery. The Persians pushing the great battering ram would marvel at their luck, an unlooked-for piece of luck which Ballista thought might give Shapur and those around him pause for thought.

Practice was improving the skills of the artillerymen of Arete. By the time the Sassanid line reached the section of white-painted wall, three of their ballistae had been squashed by high-velocity missiles. As the ram, mantlets and bowmen carried on to cross the last 200 paces to the city wall, the Sassanid artillery unlimbered and began to shoot back. Honours were even: two of the defenders' and two of the attackers' ballistae were rendered inoperable. The Dux Ripae was happy enough. This was the only area of the siege where he would win a battle of attrition. Then another thought came to his mind: Disgraceful. Men are dying – my men as well as the enemy – and I am just calculating the numbers of machines destroyed and damaged, the effects on the rate of shooting. Disgraceful. Thank the gods that war can never be reduced to this impersonal machine-against-machine battle alone. If it could, what an inhuman business it would become.

The Sassanid officers had an admirable control over their troops. The archers held their fire until the mantlets were fixed in position just fifty paces from the walls. Not an arrow was loosed until the command. When it came, the sky darkened again. As, with a terrible whistling, the arrow storm hit, Ballista once more marvelled at the almost unbelievable enormity of the thing. The defenders hunkered down behind the battlements and below their shields to weather the storm. Shouts and cries showed that not all had done so unscathed. In the pause before the next wave the bowmen of Arete leapt to their feet and sent back an answering volley.

Crouched behind the parapet, shields held all around him, Ballista knew he had to ignore the arrow storm. It was an irrelevance. Stoic philosophers held that everything that did not touch a man's moral purpose was an irrelevance. For them, death was an irrelevance: fucking fools. Ballista's only purpose was to destroy the great ram, the Khosro-Shapur.

Judging by the tortoise, the ram was about sixty feet long. The head which emerged was capped with a metal sheath, fittingly enough in the shape of a ram's head. It was bound to the shaft with nailed-down strips of metal. The wooden shaft itself looked to be about two feet thick. Like the tortoise it was covered in dampened rawhides.

With suicidal courage, eastern warriors ran ahead to tear away the remains of the burnt siege tower and tip rubble to fill in the pit in which it had been trapped. The labourers were just twenty yards from the gate. It was hard for the Roman archers to miss. There was something deeply unnerving about the fanaticism with which the Sassanids leapt forward to replace men who had fallen – leapt forward to certain death. Were they drunk? Were they drugged?

The tortoise edged forward. The rubble in the pit shifted but took its weight. The ram neared the gate.

'Everyone, ready. Here they come. Now!' On Ballista's word legionaries stood up in the face of the arrow storm. Two near the northerner were punched backwards. Without a pause the survivors, grunting with effort, manhandled the huge, dripping-wet bags stitched together from uncured hides and stuffed with chaff over the battlement. The bags fell like massive soggy mattresses. The restraining ropes tied to the parapet snapped taut. The bags slapped wetly against the gate, held in place. Peering over, Ballista saw that he had calculated the length of the ropes exactly. The wood of the Palmyrene Gate was cushioned from the force of the ram. The sodden bags would not burn. Ballista had bought some time. Above the heads of the defenders, the arms of the three cranes swung out.

After only the briefest pause Sassanid warriors poured from the rear of the tortoise. They carried scythes tied to long poles. Through his disappointment Ballista felt a grudging admiration for Shapur and his men. They had been ready for this device. No wonder Antioch, Seleuceia and so many other towns had fallen to them in the time of troubles. These easterners were better at sieges than any barbarians Ballista had ever encountered.

Out in the open at the foot of the gate the Persians dropped like flies. As men fell others sprang out to snatch up the fallen scythes. Bloody fanatics, thought Ballista. One by one the ropes were cut. The bags began to sway and sag. He cursed himself for not thinking to use chains. Too late to worry about that now.

One by one the sodden stuffed hides fell ponderously to the ground. The wooden outer gate of Arete stood unprotected. The great ram surged forward, the horns of its head closing on the gate.

The northerner rose to his feet. He was met by a hail of missiles. With his right arm above his head, he began to guide the grapple of one of the cranes to its target; right a bit, a little more, stop, back a little, down, down, close the claws. Missiles whirled past him. An arrow embedded itself in his shield, making him stagger. Another hit the parapet and ricocheted past his face. The grapple caught the ram just behind its metal head. Ballista signalled for the crane to lift. The chains clanged rigid. The arm of the crane groaned. The grapple slipped a fraction, then held its grip. The head of the ram began to lift slowly, to point impotently towards the sky.

For a moment it looked as if it would work. Then suddenly the claws lost their grip. The grapple slid off. The head of the ram fell free. Again it pointed at the gate. Again the tortoise moved forward until it almost touched the gatehouse. There was no longer any room for a grapple between the two: the opportunity had passed; the device had failed. Ballista dropped back down behind the battlements.

The metal head of the ram drew back under the tortoise, then shot out. The whole gatehouse trembled. The crash echoed down the walls. The gate still stood. The ram drew back, then struck again. Another deafening crash. Again the gatehouse reverberated. The gate still held, but a strange tortured creaking indicated that it could not last long.

With his back to the parapet, Ballista watched Antigonus and another soldier guiding the other two cranes to their target. The massive boulders swung ominously at the end of the chains as they were traversed over the tortoise. A glance at each other and the two men signalled for the boulders to be dropped. As one, the grapples released their load. After a heartbeat there was an appalling crash.

Ducking out from behind cover, Ballista saw at a glance that the tortoise still stood. The boulders had bounced off. The arms of the two cranes were already swinging back over the wall to collect their next load. A Sassanid artillery stone took Antigonus's head off. Without even a fractional pause another soldier stood up to take his place.

The great ram struck again. The tremor came up through Ballista's boots. There was a terrible sound of rending wood. Khosro-Shapur had triumphed again: the outer Palmyrene Gate was reduced to firewood. A cheer started up from the Sassanids working the Fame of Shapur. It faltered and died. They had expected, they had been told, they would be looking down a corridor to another less strong wooden gate. They were not. They were looking at a closely cemented stone wall.

The arms of all three cranes, boulders swinging, arched back out over the gatehouse. Again Ballista stepped into the maelstrom to guide one – right, right, a bit further – Maximus and two of the equites singulares trying to cover him with their shields. An arrow caught one of the guardsmen in the throat. He fell back and his blood splashed over the group. It stung Ballista's eyes. The three grapples released their burden. A thunderous, splintering impact, and two of the boulders smashed through the roof of the tortoise, exposing its soft innards and the men below. Ballista dropped back into cover. There was no point in playing the hero unnecessarily. Maximus and the remaining guardsman landed half on top of him.

There was no need for further orders. Ballista could smell the pitch and the tar. Everything combustible that could be shot or thrown from the walls was being aimed at the yawning hole in the roof of the tortoise. Wishing they had some naptha left to make sure, Ballista closed his eyes, tried to steady his breathing and hands.

'Yes, yes, yes!' Opening his eyes, Ballista saw Maximus peering round the stone crenellations. The Hibernian was punching the air. 'It's burning – burning like a Christian in Nero's garden.'

Ballista looked up at his draco flying above the gatehouse. With the south wind hissing into its metal jaws, its white windsock body was writhing and snapping like a serpent. The incoming missiles had slackened. Maximus had been joined by Mamurra and they were looking over the battlements. Demetrius and Bagoas were huddled on the floor. The Greek boy was very pale. Ballista patted him, as if he were soothing a dog.

'They have had enough. They are running'. Maximus and Mamurra rose to their feet. Ballista stayed where he was.

Inexplicably, a group of girls appeared on the roof of the gatehouse. They were wearing very short tunics and a lot of cheap jewellery. There were no more incoming missiles. Ballista watched the girls walk to the battlements. They stood in a line giggling. All together they lifted their tunics around their waists. Baffled, Ballista stared at a row of fifteen naked girls' bottoms.

'What the fuck?'

Mamurra's slab-sided face cracked into a great grin. 'It is the third of May.' Seeing complete incomprehension on Ballista's face, the praefectus fabrum went on, 'the last day of the festival of the Ludi Florales, when traditionally the prostitutes of the town perform a striptease.' He jerked his thumb in the direction the girls were facing. 'These girls are honouring the gods and at the same time showing the Sassanids what they won't be enjoying.'

All the men on the gatehouse were laughing. Only Bagoas did not join in.

'Come on,' said Maximus, 'don't be prudish. Even a Persian like you must fancy a girl now and then, if only when he runs out of boys.'

Bagoas ignored him and turned to Ballista. 'Showing the bits that it is not proper to see is an omen. Any mobad could tell you. It portends the fall of this town of the unrighteous. As these women disclose their secret and hidden places to the Sassanids, so shall the city of Arete.'

For a day and a night a column of black oily smoke streamed away to the north as the Khosro-Shapur, the Fame of Shapur, burnt. The flames from the great ram and its tortoise lit the dark.

For seven days the Sassanids gave themselves over to their grief. Day and night the men feasted, drank, sang dirges and danced their sad dances, lines of men slowly turning, arms around each other. The women wailed, rent their clothes and beat their breasts. The sounds carried clear across the plain.

Then, for two months, the Persians did nothing _ at least nothing very active in the prosecution of the siege. They did dig a ditch and heap a low bank around their camp; there was no wood to build a palisade. They stationed mounted pickets beyond the north and south ravines and on the far side of the river. Parties of cavalry rode out presumably to reconnoitre or forage. On occasional moonless nights, small groups would creep on foot close to the city and of a sudden release a volley of arrows, hoping to catch an unwary guard or two on the city wall or some pedestrians in the streets beyond. Yet, for two months, the Sassanids ventured no more assaults, undertook no new siege works. Throughout the rest of May, all of June and into July, it was as if the easterners were waiting for something.

What am I doing here? The thoughts of Legionary Castricius were not content. It is the twenty-fourth of May, the anniversary of the birthday of the long-dead imperial prince Germanicus – to the memory of Germanicus Caesar a supplication. It is my birthday. It is the middle of the night, and I am hiding in some damp undergrowth.

A cool breeze blowing across the Euphrates from the north-east rustled the reeds. There was no other sound but the great river rolling past, gurgling, sucking at the banks. There was a strong smell of damp earth and rotting vegetation. Up above, tattered clouds no more covered the moon than a beggar's cloak. Just in front of Castricius's face a spider's web was silvered in the moonlight.

It is my birthday, and I am cold, tired, scared. And it is all my own fault. Castricius shifted slightly, lifting one wet buttock from the ground, and was shushed by the man behind him. Fuck you, brother, he thought, settling down again. Why? Why am always such a fool? A keen little optio like Prosper asks for volunteers – could be a bit dangerous, boys – and my hand goes up like a whore's tunic. Why do I never learn? Why do I always have to prove that I am the big man, up for anything, scared of nothing? Castricius thought back across the years and the many miles to his school-teacher in Nemausus. You will end on a cross, the paedagogus had often said. So far he was wrong. But Castricius had been sent to the mines. He suppressed a shudder thinking about it. If I can survive the mines, I can survive anything. Moonlight or no moonlight, tonight will be a walk in a Persian paradise compared with the mines.

The soldier in front turned and, with a gesture, indicated that it was time to go. Castricius got stiffly to his feet. Crouching, they moved south through the reed beds. They tried to move quietly, but there were thirty of them: mud squelched under their boots, metal belt fittings chinked, a duck, disturbed by their passage, took off in an explosion of beating wings. And the wind is at our backs, carrying the noise down to the Persians, thought Castricius. Moonlight, noise and an inexperienced officer _ this has all the makings of a disaster.

Eventually they reached the rockface. The young optio Gaius Licinius Prosper gestured for them to start climbing. If I die to satisfy your ambitions, I will come back and haunt you, thought Castricius as he slung his shield on his back and began to ascend. Since the young optio had foiled the plot to burn the granaries he had made little secret of his ambition. Down by the river the far cliff face of the southern ravine was quite steep. It was this that had attracted the attention of Prosper: 'The Sassanids will never expect a night raid from that quarter.' Well, we will soon find out if you are right, young man.

Castricius was one of the first to the top. Heights held no fears for him and he was good at climbing. He peered over the lip of the ravine. About fifty paces away was the first of the Persian campfires. Around it he could see the huddled shapes of men wrapped in cloaks sleeping. There was no sign of any sentries. From some distance came the sounds of talking, laughter, snatches of song. Nearby, there was no sign of anyone awake.

When the majority had caught up, Prosper just said, 'Now'. There were an undignified few moments as everyone scrambled over the edge of the ravine, rose to their feet, slid their shields off their backs, drew their swords. Miraculously, the Sassanids slept on.

With no further word of command, the ragged line of volunteers set off across the fifty moon-washed paces to the campfire. Maybe, just maybe, this is going to work, thought Castricius. Along with the others, he accelerated into a run. He chose his man: a red cloak, hat pulled down over face, still not stirring. He swung his spatha.

As the blade bit, Castricius knew that it was all about to go horribly wrong: they were in a trap, and he was very likely to die. The blade sliced through the man-shaped bundle of straw. Automatically, Castricius sank into a very low crouch, shield well up – and not a moment too soon, as the first volley of arrows tore through the Roman ranks. Arrowheads thumped into wooden shields, clanged off chainmail coats and metal helmets, punched into flesh. Men screamed.

A blow to his left temple sent Castricius sprawling. It took him a moment or two as he retrieved his sword and got back to his feet to realize that it was an arrow, that they were caught in a crossfire.

'Testudo, form testudo,' shouted Prosper. Bent very low, Castricius shuffled towards the optio. An arrow whipped past his nose. Near him a man was sobbing and calling in Latin for his mother.

A trumpet sounded, clear and confident in the confusion of the night. The arrows stopped. The Romans looked around. There were about twenty of them left, in a loose knot rather than a parade-ground testudo.

The trumpet sounded again. It was followed by a rising chant: 'Per-oz, Per-oz, Victory, Victory.' Out of the darkness swept a wave of Sassanid warriors. The firelight glittered on the easterners' armour, on the long, long blades of their swords, and in the murderous look in their eyes.

'Fuck me, there are hundreds of them,' said a voice.

Like a wave crashing on a shore, the Persians were on them. Castricius parried the first blow with his shield. He swung his spatha low, palm up in from his right. It swung under his opponent's guard, biting into the man's ankle. The impact jarred back up Castricius's arm. The Sassanid fell. Another took his place.

The new enemy swung overhead. As Castricius took the blow on his shield, he felt and heard it splinter. From his left a Roman sword darted forward and tried to take the Persian in the armpit. Sparks flew and the point of the blade glanced off the easterner's mail. Before Prosper could pull back from the blow, another Sassanid blade flashed in and severed his right hand. Castricius watched horrified as the young optio spun round and sank to his knees, his left hand holding the stump of his right arm, his mouth open in a soundless scream. There was blood everywhere. The two Sassanids moved to finish the officer. Castricius turned and ran.

Boots stamping on the rock, Castricius flew back towards the edge of the cliff. He threw away his shield, dropped his sword. As he neared the lip of the ravine he threw himself sideways and down, sliding the last few yards, swinging his legs out first into space, twisting his body, his fingers scrabbling for purchase. For a moment he thought he had misjudged it, that he would slip backwards clear over the edge. The cliff had a hundred-foot drop here. If he fell he was dead. Sharp strong pain as his fingernails tore, but he had a grip. Sliding, scrabbling, boots missing toeholds, legs often dangling, he shinned down the face of the ravine.

High on the south-west tower of Arete, although he was at least 400 paces away, Ballista saw the trap close quicker than some of those caught in its jaws; the twang of bowstrings, the screams of men, the two clear trumpet blasts.

'Bugger,' he said succinctly.

'We must help them,' Demetrius blurted.

Ballista did not reply.

'We must do something,' the Greek boy continued.

'Sure it would be good,' said Maximus, 'but there is nothing to be done. It will all be over by the time we get any troops there. And, anyway, we cannot afford to lose any more men.'

Ballista watched for a while in silence, then said that they should go to the southern wicket gate, in case there were any survivors. Climbing down the steps from the Porta Aquaria, the northerner turned things over in his mind.

Ballista had been driven by the words dinned into him by his mentors in fieldcraft: a passive defence is no defence at all. An inactive defence not only hands all the initiative, all the momentum to the besiegers, it undermines the defenders' discipline, their very will to resist. So, since the burning of the ram, Ballista had quite frequently sent out small nocturnal raiding parties. But his heart had somehow not been in it.

The death of Antigonus had changed things. In Antigonus he had lost a master of clandestine operations. How the northerner missed him. Ballista thought back to the masterly way in which Antigonus had wiped out the Sassanids left stranded on the island in the Euphrates after the first failed assault on the city: twenty dead Persians, and not one Roman had fallen. Among the high reeds that night, death had come to the terrified easterners with bewildering speed and efficiency. The raiders Ballista had sent out since had tried their best, but the results had been mixed. Sometimes they were spotted and the mission abandoned near the start. As often as not they took as many casualties as they inflicted. And now, tonight, there was this unqualified disaster. Whatever the textbooks said, whatever the doctrines of his mentors, Ballista would send out no more raids.

Ballista stood by the open wicket gate and thought of Antigonus. It was strange how in a very brief time he had come to rely on him. It was one of the strange things about warfare – it quickly formed strong bonds between unlikely men, then with death it could even more suddenly break them. Ballista remembered the artillery ball taking off Antigonus's head; the decapitated corpse standing for a few moments, the fountain of blood.

Lungs burning, limbs aching, sweat running into his eyes, Castricius plunged on through the reed bed. He had hurled away his helmet, ripped off his mail coat when he reached the foot of the cliff. In flight lay his only hope of safety. On and on he ran, the date palms waving above his head, stumbling as roots twined round his legs. Once he fell full length in the mud, the breath knocked out of him. Fighting the exhaustion and despair that told him just to stay where he was, he struggled to his feet and plunged on.

With no warning, Castricius was clear of the reed beds. Ahead in the moonlight was the bare rock floor of the ravine; on the far side of it a group of torches along the low wall and around the wicket gate. There was no sound of pursuit. He set off at a run nevertheless. It would be a shame to get this far, so close to safety, and then be cut down.

They heard him coming before they saw him; the rasping breath, the dragging footfall. Into the circle of torchlight stumbled an unarmed man covered in mud. His hands were bleeding.

'Well, if it is not the tunnel rat Castricius,' said Maximus.

As spring turned to summer, deserters crawled through the ravines or slunk across the plain in both directions. It was a feature of siege warfare that never failed to amaze Ballista. No matter how futile the siege, some defenders would flee to the besieging army. No matter how doomed the fortress, some of the attackers would risk everything to join the encircled men. Demetrius said that he remembered reading in Josephus's Jewish War that there had even been deserters from the Roman army into Jerusalem just days before the great city was captured and burnt. Of course there was an obvious explanation. Armies consisted of a very large number of very violent men. Some of these would always commit crimes that carried the death penalty. To avoid death, or just postpone it for a short time, men would do the strangest things. Yet Ballista could not help but wonder why these men, especially among the besiegers, did not instead try to slip away and hide, try to find somewhere far away where they might be able to reinvent themselves.

There was a trickle of Sassanid deserters into Arete, never more than twenty, although it was suspected that others had been quietly despatched by the first guards they encountered. They were a great deal of trouble. Ballista and Maximus spent a lot of time interviewing them. Bagoas was emphatically not allowed to talk to them. It proved impossible to distinguish between the genuine asylum seekers and the planted spies and saboteurs. In the end, having had a few of them parade along the wall in an attempt to upset the besieging army, Ballista ordered all of them locked up in a barracks just off the campus martius. It was an unwanted extra problem. Ten legionaries from the century stationed there in reserve, that of Antoninus Posterior, had to be detailed to guard them. They had to be fed and watered.

Initially, larger numbers slipped out of Arete. This soon stopped. The Sassanids had a summary way with them. Along the plain, tapering wooden stakes were erected. The deserters were impaled on them, the spike through the anus. It was meant to be horrific. It succeeded. Some of the victims lived for hours. The Sassanids had placed the stakes just within artillery range, taunting the Romans to try to end the suffering of those who had been their companions. Ballista ordered that ammunition not be wasted. After the corpses had hung there for a few days the Sassanids took them down and decapitated them. The heads were shot by artillery back over the walls of the town, the bodies thrown out for the dogs.

If there was a motive beyond an enjoyment of cruelty for its own sake, Ballista assumed that the Sassanids wished to discourage anyone from leaving Arete to keep the demand for food in the town as high as possible. If the Persians hoped in this way to cause supply problems, they would be disappointed. Ballistas' stockpiling in the months before the siege had worked well. With careful management, there was enough food to last until at least the autumn.

The relative abundance of supplies was augmented by the arrival of a boat carrying grain. It was from Circesium, the nearest Roman-held town upriver. The passage of fifty or so miles had not been without incident. Sassanid horsemen were out in force on both banks. Luckily for the crew, the Euphrates, although winding, was wide enough to be beyond bowshot for most of its course here if one kept to the middle passage. The boat tied up opposite the Porta Aquaria on 9 June, ironically enough the festival of the vestalia, a public holiday for the bakers.

The crew was somewhat put out. Having run considerable risks, it had been hoping for a more voluble reception. Yet, in many ways, the arrival was something of a disappointment to the beleaguered garrison of Arete. Additional grain was welcome but not essential. When the boat was sighted the general expectation was that it was full of reinforcements. The crew of ten legionaries seconded from Legio IIII was a very poor substitute.

Never really having expected more men, Ballista had been hoping for letters. There was one. It was from the governor of Coele Syria, the nominal superior of the Dux Ripae. It was dated nearly a month earlier, written en route for Antioch _ 'Well away from any nasty Persians' as Demetrius acidly commented.

The letter contained self-proclaimed wonderful news. The emperor Gallienus, having crushed the barbarians on the Danube, had appointed his eldest son, Publius Cornelius Licinius Valerianus, Caesar. The new Caesar would remain on the Danube while the most sacred Augustus Gallienius toured the Rhine. In Asia Minor the gods had manifested their love for the empire, a love engendered by the piety of the emperors, by raising the river Rhyndacus in flood and thus saving the city of Cyzicus from an incursion of Goth pirates.

There was nothing else in the governor's communication except platitudinous advice and encouragement: Remain alert, keep up the good work, disciplina always tells. Ballista had been hoping for a communication from the emperors, something in purple ink with the imperial seal that could be waved around to raise morale, something with some definite news of a gathering imperial field army, a relief column tramping towards them – possibly even something that contained a projected date for the lifting of the siege. Being informed that old-fashioned Roman virtus would always endure was less than enormously useful.

The wider picture grew worse after a private conversation over a few drinks with the legionaries from the boat put the 'wonderful news' into context. Far from crushing the barbarians on the Danube, Gallienus had had to buy peace from the Carpi, the tribe he had been fighting there, so that he was free to move to the Rhine, where the Franks and the Alamanni were causing havoc. The new Caesar was just a child, a mere figurehead left on the Danube, where real power was in the hands of the general Ingenuus. The flood waters of the Rhyndacus might have saved Cyzicus but nothing had stopped the Goths sacking Chalcedon, Nicomedia, Nicaea, Prusa and Apamea. The whole of Asia Minor was threatened. The general Felix, accompanied by the great siege engineer Celsus, had been sent to hold Byzantium. Valerian himself, with the main field army, had marched into Cappadocia to try to drive the Goths from Asia Minor.

Bad as the news of public affairs was, Ballista was more disappointed that there was no letter from Julia. He missed his wife very much. It had not been beyond the bounds of possibility that a letter written by her in Rome or from Sicily could have found its way to the eastern extremity of the imperium, to Circesium and on to the boat. With any letter Julia wrote she was bound to enclose a drawing by their son, a scribble of such abstraction that only the boy himself could tell what it depicted. It was ten months since Ballista had seen his son. Isangrim would be growing fast. Changing quickly, but hopefully not out of all recognition.

Battening down his disappointments, Ballista turned back to marshalling his meagre resources to defend the town. The ten new legionaries were assigned to the century of Lucius Fabius at the Porta Aquaria on the grounds that their experience as boatmen might be of more use there than elsewhere. Casualties had been surprisingly light on the day the great battering ram had been burnt and only a few had been lost to occasional Persian arrows or in unfortunate forays until the disaster in which the young optio Prosper died. The centuries of Legio IIII on the desert wall still mustered nearly fifty men each, the turmae of Cohors XX forty. Ballista had reinforced them with another hundred of the levy bowmen from the numerus of Iarhai. The northerner hoped that serving alongside the regulars would both instill resolve in the conscripted townsmen and encourage their expertise. He was very aware that it might go differently, that the lax discipline of the levies might infect the regulars. So far, things seemed to be going as Ballista wished, but he would have liked it if Iarhai would appear more often on the battlements. The grizzled caravan protector seemed ever less inclined to have anything to do with the military affairs of the siege.

As the season advanced to high summer the temperature grew ever hotter. From the walls of Arete mirages could often be seen shimmering out in the desert, making distances difficult to judge, masking the movement of the Persians. For a northerner, the heat was almost intolerable. As soon as clothes were put on, they were soaked in sweat. Sword belts and armour straps chafed, rubbing skin raw. But that was not the worst of it. There was dust everywhere. It got into eyes, ears, mouths, down into lungs. Everyone who was not a native of the town had a persistent hacking cough. The dust somehow penetrated into the very pores of your skin. And then there were the flies and gnats, continually buzzing and stinging, covering any morsel of food, swarming on the brim of every drink.

There were only two moments of the day when it was less than hellish to be outside. In the evening, the temperature dropped as a cooler breeze blew over the Euphrates and the sky turned briefly a lapis-lazuli blue. Just pre-dawn, the wild fowl flew and the bowl of the sky was a delicate pink before the sun was hauled free of the horizon to begin its task of punishing men.

At noon on 6 July, the first day of the festival of the Ludi Apollinares, Ballista was lying in the pool of the frigidarium avoiding the heat of the day. As the bathhouse was the private one attached to the palace of the Dux Ripae, the northerner was on his own. Castricius, his latest standard-bearer, walked in and saluted smartly.

'A large dustcloud has been spotted off to the south, our side of the river, heading this way.'

By the time Ballista had reached his accustomed post on the Palmyrene Gate the dustcloud was unmistakable. A tall, dense, isolated column, it could be caused by nothing but an enormous train of men and animals marching upriver. Most likely, the vanguard would reach the Sassanid camp by early afternoon the next day.

The Persian column made good time. By noon its forerunners could be seen approaching the camp. Line after line after line of camels stretched away as far as the eye could see. Swaying gently, all were heavily laden, some were hauling things along the ground. Ballista saw that there were next to no accompanying troops. The Sassanids were supremely confident.

'What is it? There seem to be very few armed men. That must be good.' Several soldiers smiled at Demetrius's words.

'Unfortunately not,' said Ballista. 'They already have all the warriors they need.'

'Probably more than they want,' said Mamurra. 'They outnumber us by so many they actually could do with fewer mouths to feed. And the danger of plague is always greater with a really large army.'

'Then those camels are carrying food?' Demetrius asked.

'I do not think that we are going to be that lucky.' Ballista wiped the sweat out of his eyes. 'I am very much afraid they carry timber.' The soldiers within earshot nodded gravely but, seeing that the young Greek seemed none the wiser, Ballista continued. 'One of the things that has kept us safe, kept the Persians so quiet for the last couple of months, is the lack of timber around here. What little there was we burnt before they arrived. You need wood for pretty much all siege works – to build artillery, siege towers, battering rams, ladders, mantlets, tortoises and all types of screens. You need wood for pit props if you are mining. Taking a town calls for lots of wood – unless, of course, you just offer the defenders big sacks of gold to go away.'

'If only, Dominus, if only,' said Castricius.

'Yes, indeed, Draconarius, it is a pity that the Sassanids are such bloodthirsty fuckers that they would rather impale us than bribe us.'

It took two full days before the last of the caravan arrived. The Persian camp now flowed over all the plain as far as the hills. Camels bellowed, men shouted, trumpets called. Although all seemed chaotic, some organizing principle must have been at work. Within a day, carpenters could be seen hard at work, the fires of mobile field forges were fired, and strings of unloaded camels were heading off to the north-west.

The camels returned a day later. Gangs of men could be seen unloading bricks. This time it was the praefectus fabrum, Mamurra, who explained the finer points of siege engineering to the young Greek.

'They are going to build a siege ramp to try to overtop the wall at some point. Now, a siege ramp, an agger, is mainly built up out of earth and rubble. But the soil round here is sand, spreads as easily as one of Maximus's women, so they need retaining walls. That is what the bricks are for. The reptiles have not been as idle as we thought. They have been making sun-dried bricks somewhere out of sight, probably up in one of the villages in the hills to the north-west. With all that wood they are making vinae, mobile shelters for the poor bastards who are going to have to build the agger, and artillery to try and fuck our ballistae and stop us killing them all.'

'Thucydides tells that it took the Spartans seventy days to build their siege ramp at Plataea,' said Demetrius hopefully.

'If we can delay them that long it would be good,' Mamurra replied.

'Is there nothing we can do to stop them?'

Ballista slapped a fly on his arm. 'No need for despair.' He looked closely at the squashed insect and flicked it away. 'I can think of something that might work.'

During the night of ao July the Sassanids moved their artillery, thirty ballistae, into range opposite the southern end of the desert wall. Sunrise saw them emplaced behind stout screens some 200 paces out. The artillery duel began again. By lunchtime long chains of vinae were in place, making three long tunnels, at the front of which the beginnings of the ramp began to be evident. The long period of inactivity was over. The siege of Arete had entered a new and deadly phase.

'You look like a man offering a bun to an elephant. Come on, hand it over.' Although Ballista spoke with a smile, the doctor was plainly terrified. He was a civilian. His shabby tunic suggested that he was not at the peak of his profession. He held the arrow in both hands. Or rather, he had both arms held out, palms up, the arrow resting on them. His whole demeanour said, 'This is nothing to do with me.'

Seeing that the doctor was not going to move, Ballista slowly stepped forward. Making no sudden movements, as if the doctor were a nervous horse, he took the arrow. The northerner studied it closely. In most respects it was unremarkable, about two and a half foot long, with a three-bladed and barbed iron arrowhead about two inches long. On this, blood and human tissue were still evident. As with most eastern arrows, the shaft consisted of two parts, a tapering wooden footing joined to a longer shaft of reed. For reinforcement, the join was bound with animal tendon. The shaft was decorated with bands of paint, one of black and two of red. What was left of the three feathers which made up the fletching appeared not to be coloured but a natural white. Possibly goose feathers, Ballista thought.

The arrow shaft bore various cuts and nicks, no doubt the legacy of whatever hooked and hideous instruments the doctor had employed during extraction. But what made this arrow so unusual and potentially so significant was the strip of papyrus unravelling from it. The papyrus had been bound around the very end of the shaft. The feathers of the fletching had been glued on top of it. The papyrus was some three inches long and about half an inch wide. Its inner face was covered with Greek characters written in a small, neat hand. There was no punctuation, but of course that was quite normal. Ballista tried to read it, but he could make out no words. All that emerged was a random-seeming sequence of Greek letters. He detached the coded message and handed it to Demetrius.

'Who did you dig this out of?'

The doctor swallowed hard. 'A soldier from the numerus of Ogelos, Kyrios, one of the conscripted townsmen.' The man stopped. He was sweating.

'Why did he come to you?'

'Two of his fellow soldiers brought him, Kyrios. They had taken him to the doctor of the numerus, but he was drunk.' The man stood straighter. 'I never drink to excess, Kyrios.' He beamed at Ballista. He was still sweating.

'And did you find out where he was when he was hit?'

'Oh yes, his friends told me. They said that he had always been unlucky. He was not on the wall, not even on duty. They had been drinking in The Krater all evening. They were on their way home, back to the tower just east of the postern gate. They were crossing that bit of open ground when, whoosh, out of the darkness, the arrow came down over the southern wall and hit him in the shoulder.'

'Did he survive?'

'Oh yes, I am a very fine doctor.' His tone betrayed his own surprise at this outcome.

'I can see that.' Ballista stepped towards him again. This time he came right up to him, using his size to intimidate. 'You will not mention this to anyone. If I hear that you have…' He let the threat hang.

'No, no one, Kyrios, no one at all.'

'Good. Give the soldier's name and that of his friends to my secretary and you are free to go. You have played the part of a conscientious citizen very well.'

'Thank you, Kyrios, thank you very much.' He virtually ran to Demetrius, who had his stylus ready.

There was a loud tearing sound of something big travelling fast through the air followed by a huge crash. The doctor visibly jumped. A fine trickle of plaster came down from the ceiling. The artillery duel had been going on for six days now. Clearly the doctor had no desire to be as near to it as this requisitioned house close behind the western wall. As soon as he had gabbled the names of the soldiers, he turned and fled.

Demetrius folded his writing block and hung it back on his belt. He picked up the papyrus again and studied it. To give him time, Ballista walked across the room and poured some drinks. He gave one each to Mamurra, Castricius and Maximus, put one down near the secretary and, sitting on a table, began to sip his own.

There was the awful sound of another incoming artillery stone, another crash, and again a fine drizzle of plaster. Mamurra commented that one of the Persian stone-throwers was overshooting. Ballista nodded.

At last Demetrius looked up. He smiled apologetically. 'I am sorry, Kyrios. I cannot make out the code. At least not straight away. Most codes are really very simple – you substitute the next letter in the alphabet for the one you mean and the like; sometimes even simpler: you make a small mark by the letters that are meant to be read, or you write them at a slightly different level from the others – but I am afraid that this does not seem to be so simple. If I may I will keep it and study it when I have no other duties. Maybe eventually I will unravel it.'

'Thank you,' said Ballista. He sat and drank, thinking. They all sat in silence. At intervals of about a minute there was another crash and more plaster drifted down to add to the fine dust which covered every surface.

Ballista once more felt the lack of Antigonus; he would have been ideal for what Ballista wanted done. Mamurra was already too busy; Ballista wanted Maximus with him…

'Castricius, I want you to talk to the three soldiers. Find out exactly when and where the man was hit. Swear them to secrecy. Threaten them a little to make sure they do not talk. You had better be quick talking to the wounded one before he dies of some infection.'

'Dominus.'

'Then pick three of the equites singulares and have them keep a discreet watch on the area. It is too much to hope that one of them will be hit by an arrow with a coded message tied to it, but I want to know who they see in that part of town.'

Again the standard-bearer simply said, 'Dominus.'

'Anyone hanging around there might be our traitor looking for the message he was expecting but never received. At least now we have positive proof that we still have a traitor among us.'

A crescent moon hung low on the horizon. Above, the constellations slowly turned – Orion, the Bear, the Pleiades. It was the fifteenth of August, the ides. Ballista knew that, if they were still alive to see the Pleiades set in November, they would be safe.

It was deadly quiet on the battered south-west tower of Arete. Everyone was listening. Usually it seemed unnaturally quiet in the evening when the artillery duel ceased for the day but, now, as they strained to hear one particular sound, the night outside the tower was full of noise. A dog barked somewhere in the town. Nearer at hand a child cried. Faint noises drifted across the plain from the Sassanid camp: the whinny of a horse, a burst of shouting, snatches of a plaintive tune picked out on a stringed instrument.

'There, do you hear it?' Haddudad's voice was an urgent whisper.

Ballista could not hear it. He turned to Maximus and Demetrius. In the dim light they both looked uncertain. They all continued to strain their ears. The night grew quieter.

'There, there it is again.' The voice of Iarhai's mercenary captain was even softer.

Now Ballista thought he half heard it. He stilled his breathing. Yes, there it was: the chink, chink sound Haddudad had described, gone as soon as the northerner heard it. He leant out over the parapet, cupping his hand to his right ear. The sound was gone. If it had existed at all, it was covered by the noise of a Persian patrol making its way along the southern ravine. The scatter of stones dislodged in the near darkness, the creak of leather, the clang of metal on metal – all rang loud. They must have reached a picket. The listeners on the tower heard the low challenge 'Peroz-Shapur' and the answer: 'Mazda.'

Ballista and the others shifted their positions and breathed deeply as they waited for the patrol to pass out of earshot up on to the plain.

The volume of the night resumed its normal elusive texture. An owl hooted. Another answered. And in the silence that followed, there it was: floating up from somewhere' down in the ravine towards the plain, the chink, chink, chink of pickaxe on stone.

'You are right, Haddudad, they are digging a tunnel.' Ballista listened some more until somewhere behind him in the town a door opened and a burst of laughter and raised voices obliterated any other sound.

'We should send out a reconnaissance party. Find out exactly where it starts. Then we can estimate the route it will take.' Haddudad still spoke in a whisper. 'I would be happy to go. I can pick the men in the morning and go tomorrow night.'

'Thank you, but no.' Ballista had been about to call for Antigonus. Then he remembered. He thought for some moments. 'We cannot wait until tomorrow night. If we make any preparations for a scouting party the traitor may find a way to warn the enemy. Our men would walk into a trap. No, it must be tonight, now. I will go with Maximus.'

There was a collective intake of breath, then several voices spoke at once. Quietly but determinedly Demetrius, Haddudad and his two sentries in their different ways said that this was madness. Maximus said nothing.

'I have made my decision. None of you will speak of this. Haddudad, you and your men will stay here. Demetrius, go and find me some ashes or burnt cork and meet Maximus and me at the southern postern gate.'

Haddudad and his men saluted. Demetrius hesitated for some time before going down the steps.

By the time Demetrius had fetched the camouflage from the requisitioned house that served as military headquarters and reached the postern gate, Ballista had told the plan to Cocceius, the decurion in command of the turma of Cohors XX stationed there. Ballista and Maximus were going to leave by the gate. It was to be left open until dawn. Then it was to be shut. It was not to be opened again unless the Dux Ripae and his bodyguard appeared before it in daylight, when the guard could be certain they were alone. In the event of them not returning, Acilius Glabrio was to assume command of the defence of Arete. Ballista had written a short order to this effect.

'Sure, is that not enlisting the wolf to be your sheepdog, thinking as you do that he himself might be the traitor?' Maximus had said in Celtic.

'If we do not come back, I think we will be past caring about that,' Ballista had replied in the same tongue.

Ballista prepared himself. He took off his helmet, mail coat and the two decorations on his sword belt – the mural crown and the golden bird that had been a parting gift from his mother. He tied his long fair hair in a dark cloth and, as he always wore black, had only to rub his face and forearms with burnt cork. Maximus took rather longer. He gave the many ornaments which festooned his belt to Demetrius, with a graphic threat of what he would do if the Greek boy lost any of them. As his tunic was white, he stripped it off and got help darkening his torso, heavily muscled and much scarred. With a minimum of fuss they stepped through the gate.

The two men stood just outside for a while, letting their eyes become accustomed to the light of the stars and the sliver of moon. Ballista punched Maximus softly on the shoulder. The Hibernian gently punched him back, his teeth flashing white in the darkness. A path, paler than the rock around it, snaked away down into the ravine.

With no words, they set off, Ballista in the lead, Maximus falling into step behind. They had known each other a long time; there was no need for any discussion. Maximus knew that, as was the custom among the tribes of Germania, Ballista on reaching puberty had been sent to learn the ways of a warrior with his maternal uncle. He had been a renowned war leader among the tribe of the Harii. Since Tacitus had written his Germania, the fame of the Harii as night fighters had spread far beyond the forests of the north. By preference, they fought on pitch-dark nights. With their blackened shields and dyed bodies, their shadowy and ghoulish appearance struck fear into the hearts of their enemies. Tacitus went so far as to claim that 'no enemy can endure a sight so strange and hellish'. Maximus knew that there were few more dangerous men in the dark of the night than his dorninus and friend.

After a time the path turned to the right towards the plain and, still descending, ran along the flank of the ravine. Now Ballista and Maximus were among the tombs of the Christian necropolis. Above and below the path were the black entrances to the natural and manmade caves where the worshippers of the crucified god buried their dead. Ballista stopped and made a signal with his hand. Together they climbed up the side of the ravine to the nearest mouth of a cave. Some three feet in, the tomb was sealed with a wall of mud bricks. Still without speaking, the two men squatted down, leaning their backs against the wall. They listened and watched. Twinkling watch fires could be seen at the top of the far side of the ravine. Now and then sounds wafted across, so low as to be at the limit of hearing. From the floor of the ravine nothing could be seen or heard. The sounds of tunnelling had disappeared.

After what to Maximus seemed a very long time, Ballista rose to his feet. Maximus followed suit. Ballista turned to the wall, fumbled with his clothing and urinated on the wall.

'Do you not think it might bring bad luck, pissing on their tombs?' The Hibernian's voice was very quiet.

Ballista, concentrating on missing his boots, was slow to answer. 'Maybe, if I believed in their one god. But I would rather piss here in the darkness than out there in the open.' He rearranged himself.

'If I was frightened I would not do this,' said Maximus. 'I would go and till the soil, or sell cheese.'

'If you do not know fear, you cannot know courage,' replied Ballista. 'Courage is being afraid but doing what you have to do despite it – you could call it male grace under pressure.'

'Bollocks,' said Maximus.

They set off again down to the path.

Just discernible in the dim light, other narrow paths ran off to either side. Ballista ignored the first two to the left heading downhill. He stopped at the third. After looking all around to try to judge how far they had walked, he took the left-hand turning. They were still descending but were now travelling back towards the river. As they neared the bottom of the ravine, Ballista stopped more frequently. Eventually, he signalled that they were to leave the path and climb straight down the face of the ravine.

Maximus's boot dislodged a small avalanche of stones. Both men froze. There was no alarm. Far off in the distance a jackal barked. Others of its kind joined in. Ballista had judged the risk of making a noise while climbing on hands and knees, swords slung behind their backs, less than that of walking straight down one of the paths. If he had been in command of the Sassanid guard, he would have placed a watch where the paths reached the floor of the ravine.

They reached the bottom with no further incident. Without pausing, Ballista set off to cross to the southern wall of the ravine. There was no time to lose. They already knew that Persians carrying no lights sometimes patrolled here. Holding their swords away from their bodies, they moved at a slow jog.

As soon as they reached the opposite side they began to climb. The cliff face here was steeper. They moved slowly, searching for handholds. They had not been ascending long before the gradient lessened. Ballista signalled a halt. They lay on their backs, looking all around, listening hard. There it was again, coming from their left, from further up the ravine towards the plain, the chink, chink, chink of pickaxes on stone.

Crabwise they crawled along the cliff face, taking the greatest care where they put their hands and feet. Without being told, Maximus could appreciate Ballista's thinking. The entrance to the mine would be in the north face of the ravine, tunnelling towards the wall of the town. The attention of any sentries should be directed the same way. By crossing the ravine Ballista had in effect put them behind the enemy lines. With luck, no one would notice them as they approached from an unexpected direction.

Maximus was concentrating so hard on not making a sound that he failed to see Ballista's signal and bumped into him. There was a grunt from Ballista as a boot kicked him in the calf and a sharp intake of breath from Maximus. They made no other noise as they waited.

With infinite caution Ballista half turned and gestured down and across the ravine. Equally carefully, Maximus turned. The entrance to the Persian siege mine was about halfway up the northern face of the ravine. It was lit from within by torches or lamps. In their glow the black silhouettes of miners flitted back and forth, casting grotesquely elongated shadows. The sound of pickaxes was clear. Men working pulleys and winches to remove the spoil could just be made out at the lip of the mine. Instantly, Ballista's mind was full of memories of the distant north, stories of dwarves scheming mischief deep in their rock-hewn halls. He wondered what thoughts were in Maximus's mind. Probably what was usually there – women and drink. The men toiling at the pulleys ceased work and, abruptly, some form of screen was pulled across the mouth of the tunnel.

Ballista looked away into the darkness towards the river until his night vision returned. Then, using the faint chinks of light which escaped from the screen and the looming dark outline of the town defences, lit by just a few torches, he tried to estimate the exact position of the mine. He took great pains over this; distances are harder than ever to judge at night. He could sense that, beside him, Maximus was eager to go, but he took his time. There would be no second chance. Eventually, he patted the Hibernian's arm and signalled their withdrawal.

Crabwise again, they inched back along the cliff the way that they had come. Ballista was taking extravagant care. He feared that the relief of being on the homeward journey might lead him into a false move. When he judged that they were roughly where they had climbed up, he signalled to Maximus and they descended. This time, on reaching the floor of the ravine they waited, their senses probing the darkness. Across the void the great southern wall of Arete stood out black against the skyline. It was lit here and there by a torch. Their light and warmth beckoning, the massive solidity of the wall and towers gave Ballista a pang to be safe inside once more. He shrugged it off. Inside, his war was one of endless bureaucratic book-keeping, list after list of men and supplies. Out here in the darkness was the true way of the warrior. Out here his senses were fully alive, stretched to their limits.

Nothing threatening could be seen on the floor of the ravine. Nothing heard, and nothing smelt. Ballista gave the sign. As before, they set off at a slow jog.

The two men were halfway across when they heard the approaching Sassanid patrol. They froze. The sides of the ravine were too far to make a run for it. There was nowhere to hide. The noises were getting louder: the crunch of stones under numerous boots, the slap of weapons against shields and armour.

Leaning very close to his bodyguard, Ballista whispered. 'There are too many of them to fight. We will have to talk our way out of this. You had better not have forgotten your Persian.' The Hibernian did not reply, although Ballista was sure that he was grinning. The Persian patrol was emerging from the darkness that lay down towards the river, a dim blur, darker than its surroundings.

Suddenly, without warning, Maximus stepped forward. In a low voice but one pitched to carry he called 'Peroz-Shapur.' A surprised silence succeeded the noises of the advancing Sassanids. The patrol must have stopped. It had not been expecting to be challenged at this point. After a few moments a voice, slightly uncertain, called back, 'Mazda.' Without hesitation, Maximus called in Persian, 'Advance and identify yourselves.' The noises of armed men moving resumed.

Now the dark blur began to be recognizable as made up of individual warriors. Ballista noted two on either side detaching themselves from the main body and fanning out. Admiring as he was of Maximus's bold stroke, he did not intend to trust his life to the Hibernian's talking. When the patrol was about fifteen paces away, Ballista stepped to the front and called, 'Halt there. Identify yourselves.'

The Sassanids stopped. The four on the wings had arrows notched, their bows half bent. There looked to be about ten in the main body.

'Vardan, son of Nashbad, leading a patrol of the warriors of the Suren.' The voice was one used to authority. 'And who are you? You have a strange accent.' I

'Titus Petronius Arbiter and Tiberius Claudius Nero.' At the sound of the Roman names the starlight glittered on the swords which the Sassanids drew, from the flanks bows creaked as they were pulled to maximum draw. 'Mariades, the rightful Emperor of the Romans is our master. Shapur the King of Kings himself decreed that his servant Mariades send men to reconnoitre by stealth the postern gate of the town of the unrighteous.'

There was silence for a while. Ballista could feel his heart beating, his palms sweating. At length Vardan replied. 'And how do I know that you are not deserters from the Great Emperor Mariades?' There was a wealth of scorn in 'Great Emperor'. 'Roman scum running to its own kind?'

'If we were fools enough to desert into a doomed town we would deserve to die.'

'There are many fools in the world, and many of them are Romans. Maybe I should take you back to camp to see if your story is true?'

'Do that and I will come and watch you impaled tomorrow morning. I doubt that the Mazda-worshipping Shapur, King of Aryans and Non-Aryans, will take kindly to his orders being countermanded by an officer of the Suren.'

Vardan walked forward. His men were clearly taken by surprise. They started walking hurriedly after their commander. Vardan held his long sword at Ballista's throat. The others closed round. The commander put his sword aside and peered closely into Ballista's face. The northerner returned his gaze.

'Uncover the lantern. I want to see the face of this one.' A Persian behind Vardan began to move.

'No. Do not do that.' Ballista put all his experience of command into his voice. 'The great King's mission will fail if you show a light. The Romans up on the wall could not fail to see it. Shapur will not get the information, and we will meet our deaths at the foot of that wall.'

There was an awful moment of indecision before Vardan told the lantern-bearer to remain as he was.

Vardan brought his face so close that Ballista could smell his breath; a waft of some exotic spices. 'Even in the dark with your face blackened like a runaway slave I can still see you well enough to recognize you again.' Vardan nodded to himself. Ballista did not move. 'If this is a trick, if you are in the town when it falls, I will seek you out and there will be a reckoning. It will be I that watches you writhe on the stake.'

'Mazda willing that will not happen.' Ballista took a step backwards, keeping his hands well away from his sides. 'The night is advanced. If we are to return by dawn we must be going.'

Ballista looked over at Maximus, jerked his head towards the wall and walked to the edge of the circle of Sassanid warriors. The two blocking his way did not move. He turned back to Vardan. 'If we do not return tell our master Mariades that we did our duty. Remember our names: Petronius and Nero.'

Vardan did not reply. But at his sign the two men blocking Ballista's way moved aside. Ballista set off.

It is very difficult to walk normally when you think that someone is watching you and even more difficult when you think that someone might try to kill you. Ballista forced down an urge to break into a run. Maximus, Allfather bless him, had fallen in directly behind his dominus. The Hibernian would take the first arrow. Yet Ballista's back still felt terribly exposed.

Fifty paces was about the real limit of accurate bowshot, less in a dim light. How far had they walked? Ballista started to count his steps, stumbled slightly and went back to concentrating on walking as normally as possible. The walk seemed to last for ever. The muscles in his thighs felt twitchy.

In the end, the wall of the ravine came as almost a surprise. Both men turned, crouching, making themselves the smallest target possible. Ballista realized that he was panting. His tunic was soaked in sweat.

'For fuck's sake, Petronius and Nero?' Maximus whispered.

'It's your fault. If you ever read anything apart from the Satyricon some other names might have appeared in my mind. Anyway, let's get the fuck out of here. We are not home yet. The reptiles might change their minds and be after us.'

Demetrius was standing just outside the postern gate. He was surprised to find himself there. Admittedly Cocceius the decurion and two of his troopers were there as well. But even so Demetrius was surprised by his own bravery. Part of his mind kept telling him that he could hear and see just as well, maybe better, up on the tower. He pushed such thoughts away. There was a strange exhilaration in being outside the walls after so many months.

Demetrius stood with the three soldiers, listening and watching. The dark was alive with small sounds; the scurrying of nocturnal animals, the sudden rush of wings of a night bird. The gentle wind had moved round to the south. Fragments of sound, voices, laughter, the cough of a horse, drifted across from the Persian pickets on the far side of the ravine. Once, a jackal barked and others joined in. The chink of pickaxes came and went. But there was nothing that betrayed the progress of Ballista and Maximus.

The young Greek's thoughts drifted far away to the dark plain before the walls of Troy, to the Trojan Dolon slinging his bow across his shoulders, pulling the pelt of a grey wolf around him and stealing forth to spy out the Greek camp. Things had not gone well for Dolon. Out there across the dark plain he had been hunted down like a hare by cunning Odysseus and Diomedes of the great war cry. In tears, begging for his life, Dolon had revealed how the Trojan pickets lay. It had done him no good. With a slash of his sword Diomedes had cut through the tendons of his neck. His head dropped in the dust, and his corpse was stripped of his back-strung bow and the grey wolf-pelt.

Demetrius fervently prayed that Ballista and Maximus did not share the fate of Dolon. If the young Greek had had the poetry of Homer to hand he would have tried to see how things would fall out. It was a well-known method of divination to pick a line of the Iliad at random and see what light the divine Homer shed on the future.

The thoughts of Demetrius were dragged back to the present by the sounds of a Sassanid patrol making its way along the ravine up from the river. He heard the challenge 'Peroz-Shapur' and the response, 'Mazda', then a low exchange in Persian. Demetrius found himself, like the others, on the lip of the ravine, leaning forward, straining to catch the words. It was pointless. He did not know a word of Persian.

Demetrius physically jumped as a flood of light came from the postern gate. He spun round. In silhouette in front of the gate stood Acilius Glabrio. The torchlight caught the nobleman's gilded cuirass. It was moulded to resemble the muscles of an athlete or hero. Acilius Glabrio was bareheaded. The curls of his elaborate coiffure shone. His face was in shadow.

'What in the name of the gods below is happening here?' The patrician tones sounded angry. 'Decurion, why is this gate open?'

'Orders, Dominus. Orders of the Dux.'

'Nonsense, his orders were that this gate remain shut at all times.'

'No, Dominus. He told me to keep the gate open until dawn.' The junior officer was cowed by the seemingly barely controlled anger of his superior.

'And why would he do that? To make it easy for the Persians to get in?'

'No… no, Dominus. He and his bodyguard are out there.'

'Are you mad? Or have you been drinking on duty? If you have I will have you executed with old-fashioned severity. You know what that entails.'

Demetrius did not know what that entailed, but presumably Cocceius did. The decurion started to shake slightly. Demetrius wondered if Acilius Glabrio's anger was real.

'Even our beloved Dux is not such a barbarian that he would desert his post to run around outside the walls in the middle of the night.'

Acilius Glabrio half turned. He pointed to the gate. 'You have moments to get inside and return to your post before I have this gate shut.'

Arguing with senior officers did not come easily to Cocceius. 'Dominus, the Dux is still out there. If you close the gate he will be trapped.'

'One more word from you and it is mutiny. Inside now.'

The two troopers sheepishly went inside. Cocceius started to move.

'No.' Demetrius almost shouted. 'The Dux heard the sounds of tunnelling. He has gone to spy out where the Persian mine is being dug.'

Acilius Glabrio rounded on him. 'And what have we here? The barbarian's little bum boy.' He stepped close to Demetrius. He smelt of carnations. The torchlight highlighted the little ruffs of beard that were teased out in curls from his neck. 'What are you doing here? Selling your arse to this decurion and a few of his troopers so that they open the gate and let you desert?'

'Listen to the boy, Dominus. He is telling the truth,' Cocceius said.

The intervention attracted the full attention of Acilius Glabrio. Now the young patrician's anger was palpably genuine. Turning from Demetrius, he approached the decurion. 'Have I not warned you? Inside now.'

Cocceius dared a final appeal. 'But Dominus, the Dux… we cannot just abandon him out there.'

Forgetting the sword at his side, Demetrius bent down and picked up a rock.

'Are you disobeying a direct order, Decurion?'

Demetrius felt the rock sharp and gritty in his hand. The curls on the back of Acilius Glabrio's head shone in the torchlight.

'Ave, Tribunus Laticlavius.' A voice came from beyond the torchlight.

Acilius Glabrio whirled round. His sword rasped from its sheath. He crouched, his body tense.

Two ghostly figures, blackened and streaked with dust, emerged into the circle of light. The taller pulled a cloth from his head. His long fair hair fell to his shoulders.

'I must congratulate you, Tribunus, on your diligence. Patrolling the ramparts in the dead of night, most admirable,' Ballista said. 'But now I think that we should all go inside. We have much to discuss. We have a new danger to face.'