This Romanesque defence tower is the oldest structure on the Castle Hill. It was built in the first half of the 13th c. from brick and stone. The tower is 20 metres high with walls as thick as 4 metres near the ground. A characteristic feature of Romanesque style is a pairing of two arcade openings separated by a colonette which lets sunlight into the top floor of the donjon. There is a viewing terrace on the top of the tower, which offers a spectacular panorama of the Old Town and the city.