These terraces were used to irrigate fields to grown maize and potatoes and to stabilize the mountain slope. Below the terraces the slopes are covered by dense tropical forests, called cloud forests. Construction of Machu Picchu is believed to have been started by Pachacuti (1438-1471 AD) and continued for nearly 100 years until the murder of the last Inca Emperor Atahualpa on 26 July 1533 by the Spanish conquistador Pizarro when the city was abandoned. The true purposed of Machu Picchu has never been conclusively determined, although it is believed to have been used as a retreat for Inca chiefs and their elite and/or as a ceremonial city. At an elevation of 2,430 m (~7,970-ft) the site covers 80,000 acres (~32,500 ha) and is nearly 2,000-ft above the Urubamba River which loops around its base. It has more than 3,000 steps. it is estimated that about 5,000 people must have worked to built Machu Picchu, but it could only accommodate 750 to 1,000 inhabitants in more than 150 buildings. On clear days all the nearby major peaks of the Eastern Peruvian Andes could be seen and were used in the observation of the movements of the sun, the moon and the stars. These observations were taken into account when deciding the location of buildings and the direction the doors and windows would face. All the buildings were built with granite quarried on site and the classical Inca architectural style of polished dry-stone was used to cut blocks of stone to fit tightly together without mortar using no metal tools but rock. Three levels of fit and finish were used, from a fit so tight that no knife blade can be inserted between the rocks, even four centuries after the site was abandoned. This quality of workmanship was used for important personages or for buildings used in important celestial or religious functions. Much of the architectural design and building cannot be seen, it is underground. The Inca were expert aqueduct engineers and constructed subterranean and open canals to channel natural water sources to the city which allowed an uninterrupted supply of water and self sufficiency. Machu Picchu was mistakenly called 'The Lost City of the Inca'. The Spaniards never discovered Machu Picchu and subsequently the Western World was unaware of its existence, but the descendants of the Inca and the local Indians knew about it. The American explorer Hiram Bingham III is credited with the 'discovery' of the city in 1911. Much of what he found and excavated , treasures such as ceramic vessels, silver statues, jewelry, and human bones and tools were shipped from Peru to Yale University to be studied and exhibited. There are ongoing negotiations between the university and Peru to return these items. Machu Picchu was declared a UNESCO World Heritage Site in 1983. (Sources: Tour Guide; Ministerio de Cultura, Peru brochure; Wikipedia). This picture was taken on 26 August 2014, Sig...