Machu Picchu was constructed around 1450, at the height of the Inca empire, and was abandoned less than 100 years later, as the empire collapsed under Spanish conquest. Although the citadel is located only about 50 miles from Cusco, the Inca capital, it was never found and destroyed by the Spanish, as were many other Inca sites

http://en.wikipedia.org/wiki/Machu_Picchu