The ribat in Bouna (present day Annaba), also called the Fusula Ribat, dominates the promontory of the hill with the same name and overlooks the port of the town. This defensive structure, whose typology dates from the Fatimid period, belonged to a chain of ribats marking Islamic territory along the length of the Mediterranean coast. It was concealed under the Sidi Boumerouane Mosque. Thus, through a series of transformations, the site became a veritable military-religious complex. The recent process of patrimonialization, as well as the restoration project at the complex, has revealed the structure of the ribat, leaning against the wall and essentially forming the foundations of the first mosque of the town. The aim of this article is, on the one hand, to bring new knowledge, as much technical as historical, about this fortified structure, which has largely been ignored by historical research until now, and on the other, to carry out the restoration project of this edifice, which has now been classed as national heritage.