Machu Picchu is located in Peru, South America. It is 2,430 metres above sea level. The Urubamba River below surrounds the mountain on three sides. These high elevations made any possible invasions (there were none) almost impossible. However, Machu Picchu was not only chosen by the Incas for it's defensibility, but also because building materials were easily accessible. Earthquake faults below the strcuture meant that broken rocks, which were used to build Machu Picchu.
A wall damaged by the earthquake fault when it was active.