In mid-June 838, Afshin crossed the Anti-Taurus Mountains and encamped at the fort of Dazimon, between Amaseia and Tokate, a strategically important location which the Byzantines also used as a forward staging area. A few days later, on 19 June, the vanguard of the main Abbasid army also invaded Byzantine territory, followed two days after by the Caliph with the main body. Emperor Theophilos chose to confront Afshin first, since although his army was smaller, it threatened to cut off his supply lines. On 21 July, the imperial army came into view of the Arab force, and encamped on the hill of Anzen south of Dazimon. In the ensuing Battle of Anzen, the Byzantine army attacked at dawn, and initially made good progress, but noon Afshin launched his Turkish horse-archers in a ferocious counter-attack which stymied the Byzantine advance and allowed the Arab forces to regroup. At the same time, Theophilos decided to lead reinforcements to one of his wings, and his sudden absence disquieted his troops, thinking he had been killed. The Byzantine army collapsed, with some units breaking and fleeing disorderly, while others were apparently able to retreat in good order. Theophilos himself barely escaped the battle with his guard, and was surrounded by Afshin's men on a low hill. Afshin sent for catapults to be brought up to batter the Byzantine position, but the Byzantines managed to break through the Arab lines and the Emperor escaped.