In AD 376, exactly a hundred years before the end of the Western Roman Empire, an extraordinary thing happened. An entire German nation, the Visigoths, assembled on the banks of the River Danube pleading for permission to cross the river into the Roman Empire. The reason: a terrible race of mounted nomad-warriors, the Huns, had suddenly fallen on them from the east with such ferocity and in such overwhelming numbers that the Goths were forced to seek safety across the Roman frontier. Entry was granted, and all might have been well; the Goths would probably have settled peacefully as workers on the land and recruits for the legions. But exploitation by corrupt Roman1 officials (for example, when reduced to starvation the Goths were given dogmeat in exchange for their sons sold into slavery) provoked the Goths into rebellion. In 378, at Adrianople in Thrace, they destroyed a huge Roman army, killing the Eastern emperor, Valens. (The empire had recently been split into two halves, with capitals at Milan and Constantinople.) This was Rome’s worst disaster since Cannae, where in 216 BC her forces had been massacred by Hannibal.
The danger passed, thanks to firm but diplomatic handling of the Goths by Theodosius I, Rome’s last great soldier-emperor. The empire, apparently strong and secure once more, was briefly re-united at the end of his reign, but when he died in 395 it was divided — this time permanently — between his feeble sons, Honorius (West) and Arcadius (East).
With the strong hand of Theodosius removed, inherent weaknesses showed up, and the West plunged into crisis. The Goths, under their leader Alaric, broke out and proceeded to ravage the Balkans and invade Italy. Stilicho, the West’s brilliant Vandal general, defeated Alaric time and again but always let him escape, perhaps out of reluctance to finish off a fellow German. Then, on the last day of 406, disaster struck. A vast host of German tribesmen — Vandals, Suevi, Burgundians, etc. — crossed the frozen Rhine, then poured across Gaul and into Spain. Distracted by grandiose plans to wrest the Balkans from the Eastern Empire, Stilicho failed to intervene; as a result, he fell from power and was executed. Alaric then re-invaded Italy, and in 410 captured Rome itself, only to die within the year. (The Goths soon withdrew from Italy, taking with them Honorius’ sister Galla Placidia, who was captured when Rome fell; she was eventually sold back to the Romans for half a million measures of wheat.) Denuded of troops by a usurper, Britain was instructed by Honorius to fend for itself against the depredations of Saxons, Picts, and Scots (from Ireland).
At this critical juncture for the West, the situation was stabilized and to some extent reversed by a remarkable Roman general, Constantius. His policy of persuading the German tribes to settle peacefully as federates in the provinces they had invaded had considerable success; so much so that in 421 Honorius appointed him co-emperor as Constantius III, and sanctioned his marriage to Placidia, by whom he had a son, the future Emperor Valentinian III, and a daughter, Honoria, whose scandalous involvement with the Hun king, Attila, very nearly brought the Western Empire to a premature end. (Plans for recovering Britain were indefinitely shelved.)
Unfortunately, Constantius died within months of receiving the purple. But his great work, to try to preserve the empire by forging a state of harmonious co-existence between the Romans and their German ‘guests’ (as the federates were euphemistically termed), was to be carried on by another Roman general with vision, Flavius Aetius. Their task was complicated by a religious problem. Catholic Christianity was now the official religion of the Roman state. The Germans settled within the Empire were also Christians, but of a different brand — Arian. Arianism held that Christ the Son was inferior to God the Father, a doctrine in tune with the Germans’ paternalistic society. In the eyes of Romans this made them heretics, and therefore beyond the pale.
In AD 423 (when this story begins) Honorius died without issue, and this immediately created a power vacuum. The Eastern emperor, Theodosius II, the son of Arcadius, renounced his claim to the Western throne, backing instead the next legitimate heir, Valentinian, the infant son of Constantius III and Galla Placidia. (The empress and her little son were then the guests of Theodosius in Constantinople.) Meanwhile, a usurper, Iohannes, had proclaimed himself emperor at Ravenna, which had become the Western capital. Accompanied by Placidia and Valentinian, an expedition was despatched from Constantinople to depose Iohannes, who appealed for help to Aetius. Anxious to prevent Placidia coming to power as regent for Valentinian — something he saw as potentially disastrous for the West — Aetius agreed to back Iohannes. With a large force raised from among his friends and allies across the Danube, the Huns (among whom he had lived as a hostage when a boy), Aetius set out for Italy. As spring wore towards summer in the fateful year of 425, the two armies converged in a collision course upon Ravenna.
1 From AD 212 all free inhabitants of the empire were accounted Romans.