The dynasties hitherto described were political in their origin, having generally been founded by ambitious governors or vassals. These upstarts made no pretensions to the nominal authority, which they left in the hands of the Caliph even while they forced him at the sword's point to recognise their political independence. The Sámánids and Buwayhids, Shí‘ites as they were, paid the same homage to the Caliph in Baghdád as did the Sunnite Ghaznevids. But in the beginning of the tenth century there arose in Africa a great Shí‘ite power, that of the Fáṭimids, who took for themselves the title and prerogatives of the Caliphate, which they asserted to be theirs by right Divine. This event was only the climax of a deep-laid and skilfully organised plot--one of the most extraordinary in all history. It had been put in train half a century earlier by a certain ‘Abdulláh the son of Maymún, a Persian oculist (_qaddáḥ_) belonging to Aḥwáz. Filled with a fierce hatred of the Arabs and with a freethinker's contempt for Islam, ‘Abdulláh b. Maymún conceived the idea of a vast secret society which should be all things to all men, and which, by playing on the strongest passions and tempting the inmost weaknesses of human nature, should unite malcontents of every description in a conspiracy to overthrow the existing _régime_. Modern readers may find a parallel for this romantic project in the pages of Dumas, although the Aramis of _Twenty Years After_ is a simpleton beside ‘Abdulláh. He saw that the movement, in order to succeed, must be started on a religious basis, and he therefore identified himself with an obscure Shí‘ite sect, the Ismá‘ílís, who were so called because they regarded Muḥammad, son of Ismá‘íl, son of Ja‘far al-Ṣádiq, as the Seventh Imám. Under ‘Abdulláh the Ismá‘ílís developed their mystical and antinomian doctrines, of which an excellent account has been given by Professor Browne in the first volume of his _Literary History of Persia_ (p. 405 sqq.). Here we can only refer to the ingenious and fatally insidious methods which he devised for gaining proselytes on a gigantic scale, and with such amazing success that from this time until the Mongol invasion--a period of almost four centuries--the Ismá‘ílites (Fáṭimids, Carmathians, and Assassins) either ruled or ravaged a great part of the Muḥammadan Empire. It is unnecessary to discuss the question whether ‘Abdulláh b. Maymún was, as Professor Browne thinks, primarily a religious enthusiast, or whether, according to the view commonly held, his real motives were patriotism and personal ambition. The history of Islam shows clearly enough that the revolutionist is nearly always disguised as a religious leader, while, on the other hand, every founder of a militant sect is potentially the head of a state. ‘Abdulláh may have been a fanatic first and a politician afterwards; more probably he was both at once from the beginning. His plan of operations was briefly as follows:--