Located in the valley of the Terra Maistus River, the Tomb of Giants of San Cosimo, Sa Grutta de Santu Giuanni, is located in an archaeological site of great interest. The megalithic granite construction has a 26-m semicircular exedra facade, in which the entrance to the tomb chamber opens, covered with slabs, which overall reaches about 20 meters, one of the largest in Sardinia. From the materials found in the area, the building dates back to the Middle Bronze Age. The lithic enclosures are from an unspecified period. During archaeological excavations in 1981, numerous objects, pottery, ollae, bowls, a necklace made of glass paste and glass of Mycenaean import were found, along with later Roman frequentation. Numerous remains of Nuragic settlements emerge in the vicinity of the tomb, including a miniature tomb, a second megalithic tomb “Sa Grutt’e s’Orcu,” and the nuraghi San Cosimo I and II, buried for a good part, all located a short distance from the ruins of the church of San Cosimo. The church has often been the subject of disputes with the Arburians, and when the boundary was moved in 1829, the temple remained with the Gonnese.