Between the sixteenth and seventeenth centuries, Spain built some coastal towers along the coast of Sinis of Cabras to protect the local population from raids of pirates and Moorish corsairs from the nearby North Africa.
The “Torre di S. Giovanni” (St. John's Tower), named after the nearby church of San Giovanni di Sinis, is based on the remains of a single-tower nuraghe and a Punic tower. It was built between the end of the 16th and the beginning of the 17th century on the top of the hill (50 m above sea level) overlooking the archaeological site of Tharros.
Its size is considerable: externally resembles two overlapping cylinders, has a base diameter of more than 14 m and a height, including a terrace, of 11 m, to which must be added the plinth foundation and the parapet of the place-of-arms (terrace with outdoor artillery). Also remarkable is the wall thickness, about 4 m.
The tower, which is one of the most impressive in the area, overlooks both the Gulf of Oristano and the open sea, controlling the entire coastline for a radius of 28 km and keeping visual contact with the towers of San Marco, Torre Grande, Marceddì, Capo Frasca, the Sevo and Mora. It was armed with cannons and muskets and guarded by a garrison consisting of an alcalde, a gunner and four soldiers. It performed its function until 1846