The work of Salah ad-Din who put an end to the Fatimid Khalifate of Egypt and to the Latin kingdom of Jerusalem, restored the semblance of authority to the ʿAbbasid Khalifate of Baghdad, but the following period 567-656 (= A.D. 1171-1258) saw no real reconstruction of the Khalifate: existing conditions were merely bolstered up whilst internal decay proceeded on its course. In 656 (= A.D. 1258) the Khalif finally went down before the Mongol invasion which was simply destructive in its results. It was not until two centuries later that the Ottoman Turks sweeping westwards evolved a new order from these elements of decay and founded an empire which has lasted some 500 years, receiving from the last exiled representative of the ʿAbbasids such title as he could give to the historic Khalifate, and practically re-organising the Sunni Muslim world on strictly orthodox and traditional lines so that, in spite of occasional dissentients, it generally won the esteem and loyalty of the world of Islam. XX. THE LATER HISTORY OF THE ISMAʿILIAN SECT The Fatimid Khalifate had its origin in a religious sect which professed to represent the true Islam transmitted through a line of seven Imams who alone understood the real meaning of the religion proclaimed by the Prophet Muhammad: the first of these was the Prophet’s son-in-law ʿAli, and the last Ismaʿil the son of Jaʿfar as-Sadiq or his son Muhammad, with whom, according to the earlier teaching, the line ended as the Imam passed into concealment, the leaders of the sect keeping the teaching alive and preparing the way for his return to the visible world. At a later date the leaders claimed themselves to be the Imam’s descendants, the “concealment” being no more than a hiding from the persecuting Khalifs of Baghdad, and so they were the continuers of the sacred tradition, and on this claim rested the Khalifate of Kairawan and of Egypt. It is, of course, extremely difficult to make anything like a fair estimate of the religious work and influence connected with such a movement, and especially because it professed to cover its religious teaching with a veil of secrecy, and also because, during the duration of the Fatimid Khalifate in Egypt, the historians are almost exclusively occupied with recording the political activities of the rulers and make only occasional and allusive references to the sect as a religious body. It seems possible to distinguish three different elements in the sect, (i) the philosophical element which is one of the results of Greek philosophy and especially of the teaching of Aristotle as interpreted by the neo-Platonists and represented in an oriental dress after passing through a Syrian and Persian medium. Such teaching is traditionally associated with Jaʿfar as-Sadiq, and seems to have been the real doctrine of the sect at its first formation, but that was revealed only to the initiated, and apparently it was never checked or restated in the