The caliph divided his force in two: a detachment of 10,000 Turks under Afshin was sent northeast to join forces with the emir of Malatya Umar al-Aqta and Armenian troops (the Artsruni and Bagratuni rulers of Vaspurakan and Taron respectively both participated in person in the campaign) and invade the Armeniac Theme from the Pass of Hadath, while the main army under the caliph himself would invade Cappadocia through the Cilician Gates. The advance guard of the latter was led by Ashinas, with Itakh commanding the right, Ja'far ibn Dinar al-Khayyat the left, and 'Ujayf ibn 'Anbasa the centre. The two forces would link up at Ancyra, before marching jointly on Amorium. On the Byzantine side, Theophilos was soon made aware of the caliph's intentions, and set out from Constantinople in early June. His army included men from the Anatolian and possibly also the European themes, the elite tagmata regiments, as well as the Khurramites. The Byzantines expected the Arab army to advance north to Ancyra after passing through the Cilician Gates and then to turn south toward Amorium, but it was also possible that the Arabs would march directly over the Cappadocian plain to Amorium. Although his generals advised evacuation of the city, with the intention of rendering the Arabs' campaign objective void and keeping the Byzantine army undivided, Theophilos decided to reinforce the city's garrison, with Aetios the strategos of the Anatolics, and men from the tagmata of the Excubitors and the Vigla.