Some accounts trace the descent of Obaid from Abd Allah ibn Maimun el-Kaddah, the founder of the Ismailian sect, of which the Carmathians were a branch. The Ismailians may be best regarded as one of the several sects of Shiites, who originally were simply the partisans of Ali against Omar, but by degrees they became identified as the upholders of the Koran against the validity of the oral tradition, and when, later, the whole of Persia espoused the cause of Ali, the Shiite belief became tinged with all kinds of mysticism. The Ismailians believed, for instance, in the coming of a Messiah, to whom they gave the name Mahdi, and who would one day appear on earth to establish the reign of justice, and revenge the wrongs done to the family of Ali. The Ismailians regarded Obaid himself as the Mahdi, and they also believed in incarnations of the "universal soul," which in former ages had appeared as the Hebrew Prophets, but which to the Muhammedan manifested itself as imans. The iman is properly the leader of public worship, but it is not so much an office as a seership with mystical attributes. The Muhammedan imans so far have numbered eleven, the twelfth, and greatest (El-Mahdi), being yet to come. The Ismailians also introduced mysticism into the interpretation of the Koran, and even taught that its moral precepts were not to be taken in a literal sense. Thus the Fatimite caliphs founded their authority upon a combination of political power and superstition. Abu'l Kasim, who ruled at Alexandria, was succeeded in 945 by his son, El-Mansur. Under his reign the Fatimites were attacked by Abu Yazid, a Berber, who gathered around him the Sunnites, and the revolutionaries succeeded in taking the Fatimite capital Kairwan. El-Mansur, however, soon defeated Abu Yazid in a decisive battle and rebuilt a new city, Mansuria, on the site of the modern Cairo, to commemorate the event. Dying in 953, he was succeeded by Muiz ad-Din. Muiz came to the throne just at the time when dissensions as to the succession were undermining the Ikshid dynasty. Seizing the opportunity in the year 969, Muiz equipped a large and well-armed force, with a formidable body of cavalry, the whole under the command of Abu'l-Husain Gohar el-Kaid, a native of Greece and a slave of his father El-Mansur. This general, on his arrival near Alexandria, received a deputation from the inhabitants of Fostat charged to negotiate a treaty. Their overtures were favourably entertained, and the conquest of the country seemed probable without bloodshed. But while the conditions were being ratified, the Ikshidites prevailed on the people to revoke their offer, and the ambassadors, on their return, were themselves compelled to seek safety in flight.