This reform had been accomplished in its fundamental principles in Bactria, and Auramazda had been elevated above Mithra as the creator of heaven, of the gods, and the earth, when about the middle of the ninth century B.C. the armies of Shalmanesar II. of Asshur invaded the East of Iran. About this time, or soon after, the order of Athravas was formed. It rose, on the one hand, out of the ancient families of the fire-priests, who understood the custom of sacrifice, and had preserved the efficacious prayers to Mithra, Verethraghna, Haoma, and Tistrya, to Ardviçura and Drvaçpa down to the period of the reform, so far as they came over to the new doctrine; and on the other hand, out of the race of Zarathrustra, and the families of the zealous adherents of the new doctrine, who devoted themselves to the service of religion. This order of priests, which handed down in its families the sayings of Zarathrustra and those of old days, the ancient invocations as well as those of the new teaching, took precedence of the families of the nobles, warriors, and husbandmen, though they were not separated from them by any rights of connubium or other privileges. From the whole tendency of the reform there could not be any thought of acquiring such a position as that which the Brahmans--the first created of Brahman--attained among the orders of India. When the army of Tiglath-Pilesar II. entered Arachosia about the middle of the eighth century B.C. the new doctrine had already advanced to the West. It was represented among the Medes by eminent teachers. In this region, at the time when the Medes were under the supremacy of Assyria, a priestly order grew up out of the old families of the priests or Magians, _i.e._ the powerful, and adherents of the new doctrine; the families of this order abandoned their tribal connection among the Medes, and thus formed an hereditary caste, which preserved the name already in use in the West for the priests, and became so numerous that it could be ranked as a tribe among the other tribes of the Medes. The formation of this order was already complete when, after the middle of the seventh century B.C., the Medes rebelled against the kings of Asshur.