Abbassides, caliphs of Bagdad, the third Mohammedan dynasty, founded by Abul Abbas as-Saffeh (the Bloody), who claimed the caliphate as lineal descendant of Mohammed's uncle Abbas, whence the name. He was proclaimed by his adherents at Cufah in 749, and afterward defeated and put to death the last Orami-yade caliph, Merwan II., all but two of whose family were treacherously slaughtered. He died in 754, and his descendants to the number of 36 reigned till 1258, when the last, Mostasem, was expelled from the throne by Hulaku Khan. The line includes the illustrious names of Al-Mansour, Haroun al-Rashid, and Al-Mamoun: but from the 10th century they had sunk to the position of mere spiritual chiefs of Islam, all political power being wielded by the emir el-omra, or commander-in-chief. After their deposition at Bagdad, Ahmed, a member of the family, fled to Egypt, where he was recognized as caliph, and his descendants nominally reigned there, under the protection of the Mamelukes, till 1517, when Egypt was conquered by the Turks. Motawakkel, the last caliph, was carried to Constantinople, but allowed to return to Cairo, where he died in 1538.