The former capital of the Inca Empire, Sacsayhuaman, is one of the most stunning Inca ruins, located on the northern outskirts of the old city of Cusco, Peru. It is a walled complex at an altitude of 3,701 m, built like a fortress. The site is part of the City of Cuzco, which was added to the UNESCO World Heritage List in 1983. It consists of three outer lines of gargantuan walls, 1,500 ft long and 54 ft wide, surrounding a paved area containing a circular stone structure believed to be a solar calendar. The ruins also include a 500,000 gallon water reservoir, storage cisterns, ramps, citadels and underground chambers.