Machu Picchu is tangible evidence of the urban Inca Empire at the peak of its power and achievement—a citadel of cut stone fit together without mortar so tightly that its cracks still can’t be penetrated by a knife blade.The complex of palaces and plazas, temples and homes may have been built as a ceremonial site, a military stronghold, or a retreat for ruling elites.The ruins lie on a high ridge,surrounded on three sides by the windy, turbulent Urubamba River some 2,000 feet (610 meters) below.
