The most prevalent form of these ideas occurs in the essentially Persian movement known as the _Shi`a_ or “schismatics.” These are divided into two types, both alike holding that the succession of the Prophet is confined to the hereditary descendants of `Ali the cousin and son-in-law of the Prophet to whom alone was given the divine right of the _Imamate_ or leadership. The two types differ in the meaning of this Imamate, the one group contenting itself with maintaining that `Ali and his descendants have a divine authority whereby the Imams are the only legitimate rulers of Islam and its infallible guides; of this moderate type of Shi`a is the religion of Morocco and the form prevalent about San´a in South Arabia. The other group presses the claim that the Imam is the incarnation of a divine spirit, sometimes asserting that it was only by fraud that the prophet Muhammad interposed and acted as spokesman for the divine Imam `Ali. Of this type is the Shi`a which forms the state religion of modern Persia, spreading westwards into Mesopotamia and eastwards into India. The commonest belief, prevalent in the modern Shi`a, is that there were twelve Imams of whom `Ali was the first, and Muhammad al-Muntazar, who succeeded at the death of his father the eleventh Imam al-Hasan al-Askari in 260 A.H. (= A.D. 873) was the last. Soon after his accession Muhammad Al-Muntazar “vanished” at Samárrá, the town which served as the `Abbasid capital from A.H. 222 to 279. The mosque at Samárrá is said to cover an underground vault into which he disappeared and from which he will emerge again to resume his office when the propitious time has arrived, and the place whence he is to issue forth is one of the sacred spots visited by Shi`ite pilgrims. Meanwhile the Shahs and princes are ruling the faithful only as deputies of the concealed Imam. The disappearance of Muhammad al-Muntazar took place more than a century after the fall of the `Umayyads but we have anticipated in order to show the general tendency of the Shi`ite ideas which were prevalent even in `Umayyad times, especially in Northern Persia, and did much to promote the revolt against the secularised `Umayyad rule. A curious importance also is attached to the date. The disaffection of the _mawali_ came to a head towards the end of the first century of the Muslim era. There was a general belief that the completion of the century would see the end of existing conditions, just as in Western Europe the year 1000 A.D. was expected to mark the dawn of a new world. Dissatisfaction was at its height, especially in Khurasan, and the disaffected for the most part rallied round the `Alids. The `Alid claims which did so much to overthrow the `Umayyad dynasty and indirectly led to the bringing forward of the Persian element by which the transmission of Hellenistic culture was most furthered, are best understood by the help of a genealogical table.