From the very beginning of the Sasanian Empire it was recognised that a strong central government was a necessary way to govern its vast territories. Members of the royal family were appointed as governors of provinces with a large bureaucracy. This was said to be organised following the hierarchy of Sasanian society which was strictly divided into social classes. At the top was Ardashir and his successors, ‘the King of Kings’. Next came ‘kings, the highest category of nobility who ruled kingdoms and large provinces, followed by princes, ‘great men’ and ‘free men’. The largest proportion of the population consisted of dependent peasants and slaves. So-called ‘royal cities’ were created and the system of semi-independent kingdoms of the Parthian period was replaced by a unified state administrative system. ‘Royal cities’ were the headquarters of military garrisons in newly conquered countries and later the centres of administrative districts.

By the end of the Sasanian period Iran was divided into four large military and administrative districts headed by viceroys appointed by the central government. In addition territory was further divided for taxation. There were two types of landed property – royal and temple, each under a separate department. The centralisation of administration is also reflected by the enforcing of a single state religion, Zoroastrianism.