The Mazdean system, as we first trace it in history, was the religion of the Medes, a people joined with the Persians proper under Cyrus; and the Magi or priests were one of the seven tribes of the Medes, [214] as the Levites were one of the tribes of Israel. It may then be conjectured that the Magi were the priests of a people who previously conquered or were conquered by the Medes, who had then adopted their religion, as did the Persians after their conquest by or union with the Medes. Cyrus, a semi-Persian, may well have regarded the Medes with some racial distrust, and, while using them as the national priests, would naturally not be devout in his adherence at a time when the two peoples were still mutually jealous. When, later, after the assassination of his son Smerdis (Bardes or Bardija) by the elder son, King Cambyses, and the death of the latter, the Median and Magian interest set up the "false Smerdis," Persian conspirators overthrew the pretender and crowned the Persian Dareios Hystaspis, marking their sense of hostility to the Median and Magian element by a general massacre of Magi. [215] Those Magi who survived would naturally cultivate the more their priestly influence, the political being thus for the time destroyed; though they seem to have stirred up a Median insurrection in the next century against Dareios II. [216] However that may be, Dareios I became a zealous devotee of their creed, [217] doubtless finding that a useful means of conciliating the Medes in general, who at the outset of his reign seem to have given him much trouble. [218] The richest part of his dominions [219] was East-Iran, which appears to have been the original home of the worship of Ahura-Mazda. [220]