The Cusco region must be one of the most interesting in south America for its rich past and its ancestral traditions. Its rich historical patrimony and geographical contrast will satisfy all kind of curious explorers. Nowadays, the entire Cusco region economically depends on agriculture and tourism. Cusco is the seventh most populated city in Peru. Near Cusco is the Urubamba Valley, better known as the Sacred Valley of the Incas which was a military, religious, political and agricultural centre during Inca times. Many fortresses were built on the flanks of the mountains, and these fortresses controlled access to the valley and protected it from invaders. Pisac and Ollantaytambo are considered the most important fortresses in the Sacred Valley. Further from the Sacred Valley, at 2,900 m.a.s.l., the majestic sanctuary-city of Machupicchu – the lost city of the Incas – is built atop the mountain and surrounded by tropical vegetation.