Karacahisar Castle

Karacahisar Castle, Karaca Hisar Castle or Karajahisar Castle (Turkish: Karacahisar Kalesi, Greek: Κάστρο Καρακαχίσαρ) is a ruined Byzantine castle on a plateau near the Porsuk River, southwest of Eskişehir, Turkey. It stands 1,010 metres (3,310 ft) above sea level, is surrounded by walls, and covers an area of 60,000 square meters.

The castle is integral to the foundation myth of the Ottoman Empire: according to Ottoman friendly chroniclers the castle was taken from the Byzantines in 1288 and it was here that the hutbe was first read in Osman's name. This is, however, unlikely as the region had not been under Byzantine control since latest 1180 and therefore it is more likely that the castle was taken from the Germiyanids but portrayed as a victory against Christians to depict Osman as warrior for the faith.