The Old Fortress is located on Cape Carbonara. The site in medieval times was chosen for its construction due to its optimal strategic and defensive location. Historical events relating to the Aragonese presence on the Island and in the territory of Villasimius seem to support the hypothesis of an autonomous nucleus attributable to the 14th century. Around this core were built in later ages, probably in the 16th century, the four polygonal towers, a work of military architecture. The integrative defense project can be ascribed to the plan sought by Philip II, which called for the fortification of the coasts with a system of interconnected towers to counter the now-uncontrollable landings of the Turko-Barbarians.
The supplementary work to make the structure effective against artillery attacks is dated to the last glimpses of the 16th century on the basis of two main documentary sources. The first, the Camos report from 1572, mentions the Old Fortress among the structures inspected: the second, a document from 1599, mentions the “Fortalesa Biesa de Carbonayre tower.” It is therefore conceivable that the four towers were built in the time span between the two sources.
The 1599 document also shows that the tower was included in Division IV (which runs from the slopes of Villanova Strisaili to Sarrabus). From then on it acquired an increasingly important role, performing the functions of guard and defense.