Michael the Syrian preserves the fullest account of Theophilos’ campaign of 837.1 The chronicler gives as ultimate cause for the campaign the arrival of most of the Khurramite rebels, Naṣr included, at Byzantium, where they became Christians. With their help Theophilos felt confident enough to undertake a major campaign against the Arabs. He first sent messengers to the Great Armenia to exact a tribute, threatening invasion and destruction in case of a refusal. As the Armenians did not have troops at their disposal, they complied and paid. As a consequence, Theophilos thought that everything would happen according to his wishes.