The second of two Arab dynasties of the Muslim Empire of the Caliphate (caliphs = rulers) and descended from al-Abbas, uncle of the Prophet Muhammad. It overthrew the Umayyad caliphate in AD 750 and was based in Baghdad until 1258 when it was sacked by the Mongols. The end of the Umayyad dynasty meant a shift in power from Syria to Iraq. The Abbasids' settlement in Baghdad marked the beginning of the golden age of Arabic literature. The Abbasids, of great intellectual curiosity, adapted elements of earlier high cultures and incorporated them into their own.