After the battle of Bapheus in 1302, Turkish gazis from all parts of Anatolia began raiding Byzantine territories. Byzantine emperor Andronikos II Palaiologos tried to form an alliance with the Ilkhanid Mongols against the Ottoman threat. Failing to secure frontiers by the alliance he decided to attack the Ottomans with his own army. 

The Anatolian army of the Byzantine Empire was composed of the forces of local garrisons like Adranos, Bidnos, Kestel and Kete. In the spring of 1303, the Byzantine army advanced to Yenişehir, an important Ottoman city north east of Bursa. Osman I defeated them near the pass of Dimbos on the way to Yenişehir. During the battle both sides suffered heavy casualties.