It is the oldest and most important of the defensive works erected along the Maghreb coast by the Arab conquerors, at the dawn of Islam. Founded in 796, this building underwent several renovations during the medieval period. Initially, in the shape of a quadrilateral, it is made up of four main buildings opening onto two interior courtyards. In addition to the small cells of the "warrior monks" who, while ensuring their military functions, devoted themselves to prayer and contemplation, the Ribat houses two prayer rooms, the most spacious of which now houses rare collectibles of worship. and medieval crafts. times. A hundred spiral steps provide access to the watchtower from the top of which luminous messages were exchanged at night with the towers of the neighboring ribats and which offers the visitor a superb view of the city of Monastir and its sea.