Osman Bey, upon the death of Bayhoca, son of his brother Savcı Bey, in the Battle of Mount Armenia, conquered Kulaca Hisar Castle, which is a few leagues away from İnegöl and located on the outskirts of Emirdağ. As a result of a night raid with a force of 300 people, the castle was captured by the Turks. This is the first castle conquest in the history of the Ottoman Empire. Since the Christian people of Kulaca Hisar accepted the rule of Osman Bey, the people there were not harmed.