Social Estates. There is no mention in sources of the Achaemenian and Parthian periods of the ancient division of society into estates of which we learn from the Avesta, and there is no evidence that such a division existed in the first half of the Sasanian period. That such a division existed in the subsequent period (from the 5th century on) we know from Pahlavi sources, from the works of Byzantine writers (Procopius of Caesarea) and Arab writers, and from Persian tradition.

It is equally difficult to assume either that the lack of evidence in the earlier sources (especially in the Greek sources) is merely accidental or that the well attested division of Iranian society into social estates in the later period was an entirely artificial creation of that period, with no real roots in the past. Evidently, with the appearance of a state in Iran and the emergence into the foreground of other forms of social organization, the role of this ancient division into estates markedly declined.

On the other hand, there can have been no special social-estate administration, nor did this exist in the society reflected in the Avesta. The estate-terms found in the Avesta left no trace in the living language of later times. The ancient estate of "priests" (Av. adrauan- ) apparently came very early to be denoted by the term "magian" (Iran. magu- > mog), and the ancient estate of "warriors" or "charioteers" (Av. radaestar-) was repaced by the new noble estate, azatan (in Greek documents from Iran representatives of this estate were called eleuqeroi, by association with the homonum azat, "free"). This estate might also include the "horsemen" <asabaran) of non-noble origin who served in the regular cavalry and received from the treasury allotments of land in conditional possession. The development of urban life, the crafts and trade, and the appearance of a bureaucracy must have led to still greater changes affecting the third estate, (ram, "flock"), the ancient "cultivators" (Av. vastryo.fsuyant-).

-The Cambridge History of Iran, vol. 3(2): The Seleucid, Parthian, and Sasanian Periods, ed. Ehsan Yarshater (NY: Cambridge UP, 1983), 631-632.