Machu Picchu (Old Peak) 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. 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. 100 Years ago this month it was (re)discovered and Peru is celebrating this joyous occasion with a special exhibition.