Machu Picchu, sometimes called the lost city of the Incas, was built by the Incas, possibly by the ruler Pachacutec Inca Yupanqui, around the middle of the 15th century. It may have been either a religious site or a royal retreat for the Inca emperor.
Abandoned by the Incas about 100 years after it was built, Machu Picchu was rediscovered in 1911 by an archaeologist named Hiram Bingham. In 1912, he led an expedition sponsored by the National Geographic Society and Yale University to excavate the ruins. Machu Picchu turned out to be a fairly small site, probably housing not more than 500 to 700 people.
Because many of the skeletons initially found at the site seemed to be those of women, Bingham thought that Machu Picchu may have been a sanctuary or temple for the Virgins of the Sun, a group of women who worshiped the Incan sun god. However, later analysis showed an equal number of male and female skeletons. Many historians later theorized that Machu Picchu may have been a royal estate where Incan rulers and nobility could escape a larger, crowded city and relax.
Why the Incans abandoned Machu Picchu so soon after constructing it remains a subject of conjecture to historians as of 2014. Although no evidence exists that the Spanish ever found the city, it is possible they indirectly brought about its demise through an epidemic of smallpox.