Who built Machu Picchu, what was it for, and was it really a 'lost city'?

Machu Picchu was built by the Inca in the 1400s, most likely as a royal estate for the emperor Pachacuti. It is a citadel on a mountain ridge at 2,430 metres in southern Peru, about 80 kilometres northwest of Cusco, built in the classical Inca style with finely crafted dry-stone walls. No contemporary written records confirm its purpose, so the royal-estate idea is a scholarly belief, not a documented fact.

About 750 people lived there while it was in use, and most were permanent support staff called yanaconas. Studies of skeletons and DNA show that many came from far away: the community was genetically diverse, with Andean, coastal, Ecuadorian and Amazonian ancestries. The terraces were not enough to feed everyone, so food was imported from the surrounding valleys. The site was abandoned roughly a century after it was built, likely during the Spanish conquest, and it is possible that most inhabitants died of smallpox that travellers brought before the conquistadors arrived.

Then there is the 'lost city' story. In 1911 the American explorer Hiram Bingham was led there by a villager, and found Quechua farmers already working the terraces, one of whose sons led him to the main ruins. A Peruvian, Agustín Lizárraga, had even written his name there in 1902. Bingham, looking for a different Inca city, made the place world famous, but the people who lived nearby had never lost it.

Today Machu Picchu is a UNESCO World Heritage Site, and it receives over 1.5 million visitors a year.