Entrance gate to Machu Picchu, located on a ridge above the meandering Urubamba River at 2430 m asl. The site is most commonly considered an Inca citadel in operation during the 15th and 16th Century. However, its history and functions are still the subject of debates. The place has gained international attention in the early 20th Century and has been declared a UNESCO World Heritage Site in 1983. Huayna Picchu (2693 m) prominently appears in the central background of the photo.