Collier's New Encyclopedia (1921)/Abbassides
ABBASSIDES, the name of a dynasty who possessed the caliphate for 524 years. There were 37 caliphs of this dynasty who succeeded one another without interruption. They claimed descent from Abbas, the uncle of Mohammed. The most famous caliphs of this dynasty were Almansur and Harun-al-Rashid. The last Abbasside to be caliph at Bagdad was Mustasim, who was put to death by Hulaku Khan, a Mongolian ruler of Persia, in 1258.