High Quality Content by WIKIPEDIA articles! The Battle of Bapheus (Turkish: Koyunhisar Sava ) occurred on 27 July 1302 between an Ottoman army under Osman I and a Byzantine army under George Mouzalon. The battle ended in a crucial Ottoman victory, cementing the young Ottoman state and heralding the final capture of Byzantine Bithynia by the Turks. Osman I had succeeded in the leadership of his clan in ca. 1282, and over the next two decades launched a series of ever-deeper raids into the Byzantine borderlands of Bithynia. By 1301, the Ottomans were besieging Nicaea, the former imperial capital, and harassing Prussa.