Borj al Kabir

Mahdia, Tunisia

This Ottoman fort, constructed in the late sixteenth century, was built on a the site of a formal Fatimid palace. 

It is a quadrangular fortress with built up bastions at the northwest and southeast corners, originally accessed by a single portal.  From the entrance a vaulted passage leads to a courtyard surrounded by rooms, also vaulted. An oratory at the southeast corder predates the rest of the structure. 

A second entrance was added in the 19th c. when the structure was converted to a prison.