Abbassides a name given to the third Mohammedan dynasty, the caliphs of Bagdad, which was founded by Abul Abbas, who claimed the caliphate as lineal descendant of Mohammed's uncle, Abbas (q.v.) from whom the name is derived. The Abbassides were the successors of the Ommiads, the caliphs of Damascus. Early in the 8th century the family of Abbas had acquired great influence; and Ibrahim, the fourth in descent from Abbas, obtained several successes over the Ommiads, but was captured and put to death in 747. Ibrahim's brother, Abul-Abbas, whom he had named his heir, assumed the title of caliph, and, by a decisive victory near the river Zab in 750, effected the overthrow of the Ommiad dynasty. The vanquished family was treated with such severity that Abul Abbas gained the surname of Al- Saffah, the Bloody. On the death of Abul Abbas, Al-Mansur succeeded to the throne, and founded Bagdad as the seat of the empire. The descendants of Abul Abbas to the number of thirty-six, the last of whom was Mostasem, reigned until 1258, when the dynasty was expelled by Hulaku Khan. The line includes the illustrious names of Al-Mansur, Haroun al- Rashid, and Al-Mamun, but from the 10th century they sank to mere spiritual chiefs. of Islam. After their deposition at Bagdad, in 1258, a member of the family, named Ahmed, fled to Egypt, where he was recognised as caliph, and his descendants reigned there, under the protection of the Mamelukes, until Egypt was conquered by the Turks, in 1517. Motawakkel III, the last caliph, was taken by Sultan Selim I, the conqueror of Egypt, to Constantinople, and detained there some time as a prisoner. He afterwards returned to Egypt, and died at Cairo, a pensionary of the Ottoman government, in 1538.