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 at 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.