These early sects which were generally regarded as heretical were, in most cases, reproductions of older pre-Islamic Persian and Mesopotamian religious systems, with a thin veneer of Muslim doctrine, and, in the second century of the Hijra, when they became most prominent, they were strongly tinctured with Hellenistic philosophical speculations which had already exercised a potent influence in Mesopotamia and Persia. In theory these sects were “legitimist” in their adherence to the principle of hereditary descent. Orthodox Islam accepted as a constitutional principle the leadership of an elected _khalif_ or “successor,” a natural development of the tribal chieftainship familiar to the pre-Islamic Arabs. Amongst them the chief was elected in a tribal council, in which great weight was given to the tried warriors and aged men of experience, but in which all had a voice, and choice was made on what we should describe as democratic lines, and this remained the practice in the earlier age of Islam. Such a constitutional theory was no great novelty to those who had lived under the Roman Empire, but was entirely repugnant to those educated in Persian ideas, and who had learned to regard the kingship as hereditary in the sense that the semi-divine kingly soul passed by transmigration at the death of one sovereign to the body of his divinely appointed successor. This had been the Persian belief with regard to the Sasanid kings, and the Persians fully accepted Yazdegird, the last of these, as a re-incarnation of the princes of the semi-mythical Kayani dynasty to which they attributed their racial origin and their culture. Yazdegird died in A.H. 31 (= A.D. 652), and his death terminated the male line of the Persian royal family, but it was generally believed that his daughter, Shahr-banu, was married to Husayn, the son of the fourth Khalif ʿAli, so that in his descendants by this Persian princess the claims of Islam and of the ancient Persian deified kings were combined. Historically the evidence for this marriage seems to be questionable, but it is commonly accepted as an article of faith by the Persian Shiʿites.