This borj, still called the Kasbah, is a fortress that was erected at the end of the 16th century on the site of a former Fatimid palace and is considered one of the finest specimens of Ottoman military architecture.
Founded on a quadrangular plan and later equipped with corner bastions, the building is surrounded by a powerful wall originally pierced with a single entrance (after its reassignment to use as a prison, another access was built in the 19th century). This door gives access, by an arched and bent passage, to a courtyard onto which rooms, also vaulted, overlook.
At the south-eastern corner of this courtyard, an oratory of an earlier construction which has been preserved and integrated into the building.
From the rampart walkway laid out as a terrace, there is a very fine view of the end of the Cap Mahdia promontory and, closer to the monument, of the basin of an ancient port that some specialists trace back to the Punic period.