The Abbasids, descended from Muhammed the Prophet’s uncle Abbas, came to power in 749 in a revolt against the Umayyad Caliphate.
From their capital in Baghdad, they held the caliphate from 750–1258. The early caliphate was noted for its cultural brilliance, especially under caliph Harun al-Rashid (786–809) and his son Mamun (813–833). In arts and literature, Persian cultural influence on the Abbasids was great, but so was that of ancient Hellenic learning. Mamun founded a research center called the House of Wisdom, a library, academy, and center for the acquisition, translation, and study of ancient Greek manuscripts on science and philosophy. The works of Galen, Hippocrates, Euclid, Ptolemy, Archimedes, Plato, and Aristotle were particularly prized. Because Byzantine towns and monasteries were repositories of such manuscripts they became special targets for looting on Abbasid military campaigns. Diplomatic missions were further vehicles for this transmission. Mamun sent an embassy to Emperor Leo V to acquire Greek manuscripts. The emperor Theophilos sent his patriarch, the learned John the Grammarian, to Mamun. Mamun invited the most brilliant scientist of Theophilos’s court, Leo the Mathematician, to Baghdad, but Leo refused. In the early ninth century Abbasid raids into Asia Minor culminated in 838 in the sack of Amorion, the paternal city of Theophilos. The slow decline of the caliphate began soon thereafter, marked by periods of disorder as the influence of Turkish mercenaries grew stronger. The Mongols finally ejected the Abbasids from Baghdad in 1258.
(Source: «Historical Dictionary of Byzantium», by John H. Rosser)