Ranging some 30,000km, Qhapaq Ñan, Andean Road System, is the Inca civilisation's communication, trade, and defence network of roads. It was constructed over centuries and went through some of the world's most extreme terrains, from the peaks of the Andes, at an altitude of more than 6,000m, to the coast. It runs through deserts and rainforests across the length and breadth of the Andes. The 6,000km of the Qhapac Ñan, Andean Road System has 273 component sites and was selected to show the network's social, political, architectural, and engineering achievements. This includes associated infrastructure for trade, accommodation, storage, and places of religious significance.