The ribat which is built of stone has a square plan, of 36 m side length. The corners are not flanked by cylindrical towers, except for the west/east corner, where a superb cylindrical watchtower, set on a square base, stands. It is surmounted by a lantern-turret covered with a small ceramic dome. Added by Ziyadat Allah I in 821 AD, it served as a minaret for the neighboring mosque. It was inspired by the Abbasid minaret style that spread throughout the Maghreb from the end of the 8th century AD. Semi-cylindrical towers stand in the middle of the outer walls, except on the southern side, where a rectangular porch precedes the only entrance to this small fort This entrance seems to have been inspired by entrances to the Abbasid palaces at Akheidhar and At'shân, which had a profound influence on the exterior architecture of the ribat of Sousse.
Indeed, the ribat of Sousse seems to follow the original model of the ribat of Monastir built by Harthama, the founder of many other similar military installations along the eastern front.
The entrance porch of the ribat of Sousse is surmounted by a domed room housing a defensive system, composed of stunners and machicolations and designed to throw weights and heated oil at attackers. This dome represents the oldest example of such type of domes which was later to spread throughout Ifriqya.
The porch leads to an entrance hall surmounted by a perfectly symmetrical cross-vault, confirming the survival of certain Byzantine and Roman traditions. A courtyard, which occupies the centre of the ribat, is surrounded by four porticoes the arcades of which rest on sculpted marble columns and are surmounted by a series of cross or longitudinal vaults.
The west and east wings were renovated in 1722 AD. The ground floor consists of thirty-three narrow rooms covered by long stone vaults. Access to the upper floor is via staircases that open onto a corridor surrounded by rooms on all sides except the south side, which is dedicated to the prayer hall. The latter is divided into two bays and eleven naves perpendicular to the qibla wall. This wall, which corresponds to the external wall of the ribat, is pierced with six openings that appear to be archways, allowing the faithful at any time to turn into warriors to defend the ribat. No other feature demonstrates more clearly the dual religious and military character of the ribat.