Located near Lake Titicaca in Bolivia, the millennia-old city of Tiwanaku was built almost 13,000 feet (4,000 meters) above sea level, making it one of the highest urban centers ever constructed.
Surrounded by mountains and hills, the city reached its peak between roughly A.D. 500 and 1000, growing to encompass an area of more than 2 square miles (6 square kilometers), organized in a grid plan. Only a small portion of the city has been excavated. Population estimates vary, but at its peak Tiwanaku may have had at least 10,000 people living in it.
