Ever since the establishment of the Fatimid empire in the early part of the 10th century of the Christian era the origin of its rulers has been the subject of incessant discussion and polemics. This was, for the people of the time, no idle academic question, but one of immediate political importance. The defenders of the declining Abbasid state went to great lengths to discredit the rulers of the dynamic rival caliphate in the West, denouncing them not only as rebels and heretics, but also as impudent swindlers falsely claiming to belong to the house of the Prophet, while they were in reality the offspring of one Maymūn al-Qaddāḥ. The Fatimid rulers, for their part, maintained all along that they did indeed belong to the family of Muḥammad, and traced their lineage, at least from the middle of the 10th century onwards, to Ismā‘īl, the second son and, it was claimed, only legitimate successor of the famous Shi‘ite leader Ja‘far al-Ṣādiq, the great-grandson of ‘All and of Fāṭimah, the Prophet's daughter. The Ismaili descent of these rulers became a matter of faith for their partisans, who survive to the present day, in various branches, proudly identifying themselves precisely as “Ismailis”. Historians, whether in the Muslim world or, later, in the West, have taken sides in this ancient dispute, which flares up again from time to time, often with astonishing ferocity.