The Battle of Bapheus occurred on 27 July 1299, between an Ottoman Turkish army under Osman I and a Byzantine army under Georgios Mouzalon. The battle ended in a crucial Ottoman victory, cementing the Ottoman state and heralding the final capture of Byzantine Bithynia by the Ottoman Turks.
Text from Wikipedia, licensed under CC BY-SA 4.0
The 725th anniversary falls on July 27, 2027.