Hence we may assume that the doctrine of Zarathrustra had reached the West of Iran at the time when Phraortes united the tribes of the Medes (about 650 B.C.), and was known among the Medes when they were still living under their tribal chiefs and paid tribute to Asshur, or, in case of refusal, were attacked by the Assyrian armies, which, as we ascertained from the inscriptions of the kings of Asshur, was the case from the time of Tiglath Pilesar II. to the time of Assurbanipal, _i.e._ from the middle of the eighth to the middle of the seventh century B.C. A statement in Herodotus seems to lead us still further back. He calls the Magians a race or tribe of the Medes. According to his narrative this tribe was in existence in the time of Deioces, _i.e._ about the year 700 B.C. Herodotus could only speak of the Magians as a tribe or family when they had become an hereditary order. At that time, therefore, there must have been among the Medes a priesthood who perpetuated in their families their worship by sacrifice, their doctrine and wisdom, as well as their social importance. Like all Greeks, Herodotus ascribes the discharge of the religious functions among the Persians and Medes to the Magians, and we find that what Herodotus quotes of their rites agrees with the rules of the Avesta. The rise and separation of a peculiar order of priests, their more or less sharply marked distinction from the remaining orders, can never be the work of a short space of time, and such separation can only take place when the worship of the gods requires a knowledge which is not easily accessible or obtainable, when doctrine has obtained a place by the side of belief, when ritual has become developed, and particular duties and rules are prescribed for the life of the priests. When the worship of the gods requires the use of long and definite prayers, the knowledge of complicated usages, on which depends the effect of the sacrifices, and the observation of numerous rules of purification,--such knowledge is only perpetuated in families of hierophants or priests, or in schools which take the place of such families. The formation of a distinct hereditary order on such grounds can hardly have occupied less than a century from the time when the doctrine, on which it is formed, was introduced. Hence we may assume that the doctrine known as Zarathrustra's reached the Medes before the year 750 B.C., _i.e._ before the date of Tiglath Pilesar II. of Assyria.