If we may assume that the Arian character was in use in the East of Iran about the year 800 B.C., the prayers and sayings of Zarathrustra might have been written down about this date, and the doctrine might have passed on to the West supported by written documents. But the fact that the prayers might have been written down is in no way a proof that they were so written.
It is true that at first sight it seems that the part of the law which has come down to us (the Vendidad) leads to the conclusion that it was written down long before the Persians gained the dominion over Iran, and Media became a powerful state under Cyaxares. The book does not mention the name of the Persians or the Medes, of Ecbatana or Persepolis, while Bactria is spoken of as the seat of the empire; the most westerly district mentioned in the Vendidad is Ragha in Eastern Media.[175] If we add that the book reproaches certain districts in the East, the land of the Arachoti and others, with deviations from the doctrine of Zarathrustra, and that Ragha is indeed Zoroastrian but wavering in its fidelity, we may easily conclude that the Vendidad was written when the doctrine of Zarathrustra had not as yet thoroughly penetrated the East, and was still unknown in the West, when it had just reached, but had not yet completely conquered, the district of Ragha. The Medes were still dependent on Asshur, living separately according to their tribes, Ecbatana was not yet the centre and metropolis of Media, and the kingdom of Bactra was still in existence in the East. This points to a date about 750 B.C. as the time when this doctrine must have spread widely over Media; at any rate to a date before the rise of the Median power, _i.e._ before 650 B.C. This conclusion is not, however, absolutely certain. The silence of the Vendidad and of the Avesta generally on Ecbatana and Persepolis, the Medes and the Persians, can be explained in another though a more artificial manner. The nations and chief cities of the West were unknown to the tradition of Eastern Iran, and the royal abodes of the Medes and Persians were not consecrated by the action of Zarathrustra. In the accounts given by the Greeks of the worship of these nations, in spite of much agreement, points are found at variance with the rules of the Avesta, and as a fact certain distinctions did prevail. The doctrine had arisen in the East, and the priesthood there was in possession of the purer and more orthodox dogma. If Persia and Media did not follow this in all respects, it was convenient to be silent about the differences in the time of the Achæmenids, or if any one desired to brand them, to mark out the Median Ragha as the seat of heresy, rather than Pasargadæ or Persepolis. This explanation it is true is somewhat far fetched. The result that the religion known by the name of Zarathrustra had reached the Medes and Persians by the middle of the eighth century B.C. is in no way weakened by it, though the assumption that at this period written documents of this doctrine were in existence, and that the book of the law of which we have fragments arose in the first half of the eighth century B.C., is rendered more doubtful if such a mode of interpretation is admitted.