 In July – September 830, al-Ma 'mun, encouraged by perceived Byzantine weakness and suspicious of collusion between Emperor Theophilos 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 a number of 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 crossed the Cilician Gates and divided into three columns, with the Caliph, his son Abbas, and Abu Ishaq at their head. The Abbasids seized and destroyed several minor forts and the town of Tyana, while Abbas even won a minor skirmish against Theophilos in person, before withdrawing to Syria in September. In 832 al-Ma'mun repeated his invasion of the Byzantine borderlands, capturing the strategically important fortress of Loulon, a success that consolidated Abbasid control of both exits of the Cilician Gates. So encouraged was al-Ma 'mun by this victory that he repeatedly rejected Theophilos' ever more generous offers for peace, and publicly announced that he intended to capture Constantinople itself. Consequently Abbas was dispatched in May to convert the deserted town of Tyana into a military colony and prepare the ground for the westwards advance. al-Ma 'mun followed in July, but he suddenly fell ill and died on 7 August 833.
