Abbasid caliphate

Islamic dynasty (750-1258) founded by Abu al-Abbas. Beginning as a revolutionary opposition, the Abbasids overthrew the Umayyad caliph at the Battle of the Zab and transferred the center of Islamic power from Damascus to the newly founded city of Baghdad. The first phase of Abbasid history (750-945) saw the gradual erosion of the caliphs' political authority as power was delegated to military commanders; in the second phase (945-1258), the caliphate maintained only nominal and moral authority while the real power rested with secular dynasties.