Machu Picchu is a pre-Columbian 15th-century Inca site located 2,430 metres (7,970 ft) above sea level. It is situated on a mountain ridge above the Urubamba Valley in Peru, which is 80 kilometres (50 mi) northwest of Cusco and through which the Urubamba River flows. Most archaeologists believe that Machu Picchu was built as an estate for the Inca emperor Pachacuti (1438–1472). Often referred to as the "Lost City of the Incas", it is perhaps the most familiar icon of the Inca World. Machu Picchu was declared a Peruvian Historical Sanctuary in 1981 and a UNESCO World Heritage Site in 1983.