Hiram Bingham III Stuart McNairn whose descendants claim that they had already climbed to the ruins in 1906). Also the Cusco explorers Enrique Palma, Gabino Sanchez and Agustín Lizarraga are said to have arrived at the site in 1901. Bingham returned to Peru in 1912, 1914 and 1915 with the support of Yale and the National Geographic Society. In "The Lost City of the Incas" (1948), Bingham related how he came to believe that Machu Picchu housed a major religious shrine and served as a training center for religious leaders. Modern archaeological research has since determined that the site was not a religious
Machu Picchu zone exists above the area. UNESCO is considering putting Machu Picchu on its List of World Heritage in Danger. During the 1980s a large rock from Machu Picchu's central plaza was moved to a different location to create a helicopter landing zone. In the 1990s, the government prohibited helicopter landings. In 2006, a Cusco-based company, Helicusco, sought approval for tourist flights over Machu Picchu. The resulting license was soon rescinded. Authorities have struggled to maintain tourist safety. Tourist deaths have been linked to altitude sickness, floods and hiking accidents. UNESCO received criticism for allowing tourists at the location given high