About the middle of the ninth century the state of the Moslem Empire was worse, if possible, than it had been in the latter days of Umayyad rule. The peasantry of ‘Iráq were impoverished by the desolation into which that flourishing province was beginning to fall in consequence of the frequent and prolonged civil wars. In 869 A.D. the negro slaves (_Zanj_) employed in the saltpetre industry, for which Baṣra was famous, took up arms at the call of an ‘Alid Messiah, and during fourteen years carried fire and sword through Khúzistán and the adjacent territory. We can imagine that all this misery and discontent was a godsend to the Ismá‘ílites. The old cry, "A deliverer of the Prophet's House," which served the ‘Abbásids so well against the Umayyads, was now raised with no less effect against the ‘Abbásids themselves. [Sidenote: The Fáṭimid dynasty founded by the Mahdí ‘Ubaydu’lláh (909 A.D.).] ‘Abdulláh b. Maymún died in 875 A.D., but the agitation went on, and rapidly gathered force. One of the leading spirits was Ḥamdán Qarmaṭ, who gave his name to the Carmathian branch of the Ismá‘ílís. These Carmathians (_Qarámiṭa_, sing. _Qirmiṭí_) spread over Southern Persia and Yemen, and in the tenth century they threatened Baghdád, repeatedly waylaid the pilgrim-caravans, sacked Mecca and bore away the Black Stone as a trophy; in short, established a veritable reign of terror. We must return, however, to the main Ismá‘ílite faction headed by the descendants of ‘Abdulláh b. Maymún. Their emissaries discovered a promising field of work in North Africa among the credulous and fanatical Berbers. When all was ripe, Sa‘íd b. Ḥusayn, the grandson of ‘Abdulláh b. Maymún, left Salamya in Syria, the centre from which the wires had hitherto been pulled, and crossing over to Africa appeared as the long-expected Mahdí under the name of ‘Ubaydu’lláh. He gave himself out to be a great-grandson of the Imám Muḥammad b. Ismá‘íl and therefore in the direct line of descent from ‘Alí b. Abí Ṭálib and Fáṭima the daughter of the Prophet. We need not stop to discuss this highly questionable genealogy from which the Fáṭimid dynasty derives its name. In 910 A.D. ‘Ubaydu’lláh entered Raqqáda in triumph and assumed the title of Commander of the Faithful. Tunis, where the Aghlabites had ruled since 800 A.D., was the cradle of Fáṭimid power, and here they built their capital, Mahdiyya, near the ancient Thapsus. Gradually advancing eastward, they conquered Egypt and Syria as far as Damascus (969-970 A.D.). At this time the seat of government was removed to the newly-founded city of Cairo (_al-Qáhira_), which remained for two centuries the metropolis of the Fáṭimid Empire.[505] [Sidenote: The Ayyúbids (1171-1250 A.D.).]