The Museum courtyard is dominated today by the medieval tower that is believed to have been built in the late 13th century by the lord Nikolaos II Saint-Homer (1258-1294), whose family had received half the city of Thebes as a dowry from the lords of the Duchy of Athens.
It is the best preserved section of the medieval fortifications of Thebes; it is rectangular on plan with a height of 14 metres. It initially had at least three floors, of which only the first two have been preserved today. To protect it, the entrance was on the first floor with access to it and all the other levels by wooden stairs.
The tower was used as a prison in the late 19th century. On the ground floor walls, drawings have been preserved that depict prisoners counting the length of their sentence, which is unknown to us.
The recent works to support and restore the monument have brought to light significant archaeological data, on the basis of which a small exhibition has been created on the subject of the building’s function, as well as that of the other towers scattered throughout the Boeotian countryside, landmarks of the region to this day.