Italy and the most militarized island in Europe. Besides the land-occupying installations, where 80% of the military explosives in Italy are used, there are also other military structures located on the sea and along the coastline, roughly equivalent to 20000 km2 (little less than the island's surface), being made inaccessible to the civil population when military exercises are held. Among the most notable military bases on the island are the Interagency Polygons in Quirra, Capo Teulada and Capo Frasca, used by Italian and NATO forces to test-fire ballistic missiles and weapons and by Italian and European Space Agency to test space vehicles and for orbital launches. Until 2008, the US navy also had a nuclear submarine base in the Maddalena Archipelago. Depleted uranium and thorium dust from missile tests has been linked to an increase in cancers according to activists and local politicians. In the late 1980s, a high level of birth defects occurred near the Salto di Quirra weapons testing site after old munitions were destroyed. Culture Sardinia is the only autonomous region in Italy where its special Statute uses the term popolo (distinct people) to refer to its inhabitants. While this formula is also used by Veneto, which unlike Sardinia is an ordinary region, the Sardinian Statute is adopted with a constitutional law. In both cases, such term is not meant to imply any legal difference between Sardinians and any other citizen of the country. Architecture Of the prehistoric architecture in Sardinia there are numerous testimonies such as the domus de janas (hypogeic tombs), the Giants' grave, the megalithic circles, the menhirs, the dolmens and the well temples; however, the element that more than any other characterizes the Sardinian prehistoric landscape are the nuraghe; the remains of thousands of these Bronze Age buildings of various types (simple and complex) are still visible today. There are also numerous traces left by the Phoenicians and Punics who introduced new urban forms on the coasts. The Romans gave a new administrative structure to the whole island through the restructuring of several cities, the creation of new centers and the construction of many infrastructures of which the ruins remain, such as the palace of Re Barbaro in Porto Torres or the Roman Amphitheatre of Cagliari. Even from the early Christian and Byzantine epoch there are several testimonies throughout the territory both on the coasts and inside, especially linked to buildings of worship.