On 9 February 782, Harun departed Baghdad; the Arabs crossed the Taurus Mountains by the Cilician Gates, and swiftly took the border fortress of Magida. They then advanced along the military roads across the plateau into Phrygia. There, Harun left his lieutenant, the hadjib al-Rabi' ibn Yunus, to besiege Nakoleia and guard his rear, while another force, reportedly 30,000 men, under al-Barmaki (an unspecified member of the powerful Barmakid family, probably Yahya ibn Khalid), was sent to raid the rich western coastlands of Asia Minor. Harun himself, with the main army, advanced to the Opsician Theme. The accounts of subsequent events in the primary sources (Theophanes the Confessor, Michael the Syrian, and al-Tabari) differ on the details, but the general course of the campaign can be reconstructed.