The known history of Machu Picchu is rather thin, as it lacks written history from about the time of its creation until its "discovery" by a Yale graduate in 1911. Therefore, most of the city's history can only be speculated.
Probably built over a century before Spanish conquistador Francisco Pizarro undermined, divided, and conquered the Incan Empire though its actual age is unknown, Machu Picchu was rediscovered just under a century ago by U.S. explorer Hiram Bingham when a local farmer showed it to him. The few previous whites who had visited it, putting it on maps or signing a rock there, did not publicize their finding. Unfortunately, the precise age of Machu Picchu cannot be trusted from carbon dating, which has produced some consistent anomalies like labeling samples from the Mt. St. Helens' eruption as millions of years old.
From the style of the buildings, one theory of Machu Picchu's origins says that Inca Pachacuti ordered it to be built as a religious retreat in the mid-1400s, which would mean it is not a city, a theory supported by its out-of-the-way location, too distant to have much use for government, economy, or military. If it was a religious retreat, that would also explain its being "lost"—only a select few related to the emperors would have known of its existence, and small pox would have made the town too expensive to maintain. One flaw with this theory is it fails to account for beliefs that Machu Picchu was a religious sanctuary, a place of pilgrimage. It also fails to explain why Manco Inca probably burned Llatapata, the origin of the trail to Machu Picchu, while retreating after his rebellion against the Spanish in 1536.
This small Incan city is termed "lost" because the conquistadors missed it during their pillage, which suggests it might have been abandoned before the conquistadors arrived. The Incans might have also consciously chosen to hide the city from the Spaniards.
Hiram Bingham dubbed Machu Picchu the "Lost City of the Incas" when he found it, a name it has carried since as scientists study and tourists visit it.