Organization of the empire
In contrast to his father, who claimed to be “king of kings of Iran” (shāhanshāh īrān), Shāpūr I assumed the title “king of kings of Iran and non-Iran” (shāhanshāh īrān ud anīrān). This formula was retained by his successors as the regular designation of the Sāsānian emperors. The hereditary local dynasties, which under the Arsacids had ruled many of the most important provinces, were to a large extent abolished. Instead, such areas as Maishān (Mesene), in western Iran, and Sakastan (Sīstān), in eastern Iran, were now ruled by members of the Sāsānian family, who were appointed by the sovereign with the title of shāh (king). Among such provincial governors, precedence was often given to the heir to the throne, who was placed in control of large territories, such as the former Kushān empire (Kūshānshahr) and Armenia, and given the title “great king” (wuzurg shāh). This arrangement lasted until the early 4th century ad, and such emperors as Shāpūr I and Hormizd II are known to have first held the title kūshānshāh as governors of the areas of Bactria, Sogdiana, and Gandhāra. Next in the hierarchy came the few remaining hereditary vassals, such as the kings of Iberia (now Georgia) in the Caucasus, and the chief nobles of the empire, among whom the Warāz, Sūrēn, and Karēn families retained their prominent position from Parthian times. Next in line were the satraps, whose importance had diminished and who were now no more than the administrators of larger cities or court officials.
The list of provinces given in the inscription of Kaʿbe-ye Zardusht defines the extent of the empire under Shāpūr, in clockwise geographic enumeration: (1) Persis (Fārs), (2) Parthia, (3) Susiana (Khūzestān), (4) Maishān (Mesene), (5) Asūristān (southern Mesopotamia), (6) Adiabene, (7) Arabistān (northern Mesopotamia), (8) Atropatene (Azerbaijan), (9) Armenia, (10) Iberia (Georgia), (11) Machelonia, (12) Albania (eastern Caucasus), (13) Balāsagān up to the Caucasus Mountains and the Gate of Albania (also known as Gate of the Alans), (14) Patishkhwagar (all of the Elburz Mountains), (15) Media, (16) Hyrcania (Gorgān), (17) Margiana (Merv), (18) Aria, (19) Abarshahr, (20) Carmania (Kermān), (21) Sakastan (Sīstān), (22) Tūrān, (23) Mokrān (Makran), (24) Paratān (Paradene), (25) India (probably restricted to the Indus River delta area), (26) Kūshānshahr, until as far as Peshāwar and until Kashgar and (the borders of) Sogdiana and Tashkent, and (27), on the farther side of the sea, Mazun (Oman). This empire, considerably more extensive than that controlled by the Arsacid dynasty, was governed by members of the royal family and by appointed officials directly responsible to the throne. The greater degree of centralization thus attained by the Sāsānian government partly explains its increased military effectiveness in comparison with the Arsacid administration. Tight organization of the numerous central and provincial officials, whose ranks in the bureaucratic structure on different levels were strictly defined, also contributed toward general administrative efficiency.
Another trend that developed in the Sāsānian period, although it had already made itself felt under the Arsacids, was a strict principle of dynastic legitimacy. For a usurper not of the royal blood to come to the throne was an extremely rare occurrence, though it was in fact accomplished by Bahrām VI Chūbīn in 590. Loyalty was given, however, to the whole royal house, rather as it was in the later Ottoman Empire. The person of the individual ruler was a matter of comparatively lesser importance, and one member of the dynasty could readily be removed and replaced by another. In accordance with this principle of legitimacy, Persian tradition carried the Sāsānian line back to the Achaemenids and, ultimately, to the kings of the legendary period.