In July-September 830, al-Ma'mun, encouraged by perceived Byzantine weakness and suspicious of collusion between Emperor Theophilos (r. 829 - 842) and the Khurramite rebels of Babak Khorramdin, launched the first large-scale invasion of Byzantine territory since the start of the Abbasid civil war, and sacked several Byzantine border fortresses. Following his return from Egypt, Abu Ishaq joined al-Ma'mun in his 831 campaign against the Byzantines. After rebuffing Theophilos' offers of peace, the Abbasid army passed through the Cilician Gates and divided into three columns, with the Caliph, his son al-Abbas, and Abu Ishaq at their head. The Abbasids seized and destroyed several minor forts as well as the town of Tyana, while al-Abbas won a minor skirmish against a Byzantine army led by Theophilos in person, before withdrawing to Syria in September.