the name of a race who possessed the caliphat for 524 years. There were 37 caliphs of this race who succeeded one another without interruption. They drew their descent from Abbas-Ben-Abdul-Motalleb, a brother of the Prophet's father. The princes of this family made war on the dynasty of Ommiades, A.D. 746; and in 750 defeated the last caliph of the rival family in the bloody battle of Zab near Mosul. The most celebrated monarchs of this family were Al-Mansur, and Haroun-al-Raschid. Their empire terminated in Mostazem, who fell in battle against the Tartar Prince Hulaku in 1257.