The Sack of Amorium by the Abbasids in mid-August 838 represents one of the major events in the long history of the Byzantine-Arab Wars. The exceptionally large Abbasid army was led by the Caliph al-Mu'tasim (r. 833-842); who was eager to avenge the almost unopposed expedition launched by the Byzantine emperor Theophilos (r. 829-842) into the Caliphate's borderlands the previous year. The Abbasids penetrated deep into Byzantine Asia Minor; defeating the emperor at Anzen; sacking Ancyra and finally reaching Amorium鈥攁t the time one of Byzantium's largest cities and the birthplace of its ruling Amorian dynasty. The city fell after a short siege; probably by treason; and a large part of its inhabitants were slaughtered; with the remainder driven off as slaves.