An impressive iron cross stands out on the top of it and is not the only link that this fortress has with Christianity: in fact, its name evokes the memory of a medieval church that has now disappeared. The nuraghe San Pietro stands on the edge of the town of Ussaramanna, on the top of a hill surrounded by the rolling landscape between sa Jara Manna (the Giara di Gesturi) and the Giara di Siddi. It is a complex building, constructed with large sandstone blocks, in which there is a keep, standing ten metres high and with a diameter of 13 metres, surrounded by a bastion with four towers connected by a curtain wall. Three of the four lateral towers have diameters of around nine metres, while the one in the north-eastern corner is larger: its diameter is the same as that of the keep. This distinctive feature has been explained by the theory that this may originally have been a trefoil nuraghe and was subsequently modified by inserting the fourth tower.