The castle in Trembowla was built in the 14th century on a high hill over the valley of the Hniezna river. Despite its small size (100 metres by 40 metres), it was a strong fortress with walls up to 4 metres thick. After the Turks had captured Kamieniec Podolski (see Siege of Kamieniec Podolski), Trembowla was one of the few Podolian strongholds still in Polish hands.