Excavation campaigns, promoted by the City of Cagliari with the Scientific Direction of the Archaeological Superintendence, in the bastion of Santa Caterina, transformed into a square at the end of the 19th century after the defensive walls were dismantled, have made it possible to acquire important information on the frequentation of the site. During the investigations, in fact, structures and canalizations dating from the Middle Ages to the last century were found in the above-ground area; a vast underground environment, 18 meters long and about 4 meters wide, was discovered underground. The excavation revealed the existence of a site that experienced frequentation in prehistoric times and then, from Punic times to contemporary times, a long and uninterrupted life. The earliest period is documented by an Eneolithic tomb of the Monte Claro culture (2400-2100 B.C.); the large subterranean room, on the other hand, is a Punic cistern, with a thick layer of waterproofing earthenware on the floor and walls. Due to a fracture in the rocky bank, the environment suffered prolonged damage that caused the waterproofing layers to break down. The progression of the fracture determined, in the Roman period, interventions aimed at a new use; seven large rock-cut niches and four additional smaller ones at the ends were opened on the walls; the connection with the surface was made with a rock-cut staircase, equipped with an opening with a recess for a door; the dating to the 2nd century B.C./I century A.D. is provided by a mosaic fragment, at the base of the staircase. Frequentation in the late antique and early medieval ages is attested by the discovery of pottery from the 4th/7th centuries AD. It could be assumed that the building’s abandonment followed the imperial edicts closing pagan cult buildings, dated between the end of the 4th and the first half of the 5th centuries, so the idea that the hypogeum was used in late antiquity as a Christian cult building remains only a working hypothesis, pending the completion of the excavation. It will only be possible to visit the exterior.
