Arguably the most famous and iconic archaeological site in South America, the Inca city of Machu Picchu sits at an altitude of 2430m / 7,970ft on a ridge high above the Urubamba River approx 80km / 50 miles northwest of Cusco. The city was probably built during the reign of the Inca Pachacuti in the mid 15th century. It was never found by the Spanish and although the site was known about locally it was not until the American explorer Hiram Bingham arrived with an expedition from Yale University in 1911 that the site's existance was published internationally. Machu Picchu was declared a Peruvian Historical Sanctuary in 1981 and a UNESCO World Heritage Site in 1983.