The name of the sect is of doubtful origin, but Layard is inclined to a theory that it may be connected with an old Persian word meaning God.[18] The theory advanced, particularly by Shiah Muhammadans, that they were founded by Yazid,[19] the murderer of the saint Husain, is obviously untenable, and was put forward solely in order to further discredit them. The true origin of the sect is quite unknown, and the peculiarly mingled nature of their tenets makes investigation difficult. The Avesta, the sacred book of Zoroastrianism, about the 6th century B.C., mentions and execrates certain devil-worshippers, and Zoroaster himself had a campaign against similar people in north Persia. There are, in the faith of the modern Yezidis, certain indications of a connection with the ancient faith mentioned in the Avesta as being that of prehistoric peoples--a species of nature worship. But then there are equally indications of the survivals of the old Chaldean or Babylonian sun-worship, particularly in the reverence they pay to the sun, called by them Shaikh Shems, and the moon, as Shaikh Sin, corresponding to Shamash and Sin of the ancient mythology. Their customs, like their tenets, display a remarkable catholicity. They baptize, circumcise, reverence the sun and moon, carve Musulman texts upon their tombs, quote the New Testament, allow polygamy, consider wine lawful, and certain meats forbidden, a mixture of the habits of Zoroaster, Assyrio-Babylonian, Muhammadan and Christian worship unequalled by any other sect. They abhor the colour blue, and never use it in their dress nor display it in their houses. The centre and apparently original seat of these people is near Mosul, and there, in a valley of the Kurdish hills, is buried the Yezidi saint and prophet, Shaikh Adi, who is said to have lived variously in the ninth and eleventh century. Very little has hitherto been known about Shaikh Adi, the date of his existence is disputed, and his identity has not been even hinted at, except for an ingenious theory put forward many years ago, attempting to connect him with Adde, a discipline of Manes. So far we have had to be content with the assertion advanced in a Persian work that he was one of the Marwanian dynasty of Khalifas or “Caliphs,” an error easily discovered. I think, however, that the following explanation may be now accepted, the result of investigations in various Muhammadan works, to the authors of which he is well known. From these the writer has extracted the information that Shaikh Adi was the son of Musafiru’ Zahid, of the family of Ummaya, a native of Baalbek in Syria. In the reign of Marwan (early eighth century), he “was transferred” to Mosul,[20] and resided in the towns of the great Kurdish tribe of Hakkari, where his great sanctity gained him a large following among the peoples there residing.