Cahokia Mounds is a State Historic Site, a National Historic Landmark, and in 1982 became a UNESCO World Heritage Site. It is the largest prehistoric Indian community north of Mexico, covering 5-6 square miles, with 120 mounds, and a population at its peak of 10-20,000 people. 100 foot-high Monks Mound is the largest prehistoric earthwork in the Americas. The Woodhenge sun calendar has been reconstructed at the original location. A world-class museum tells the story of this ancient city and its inhabitants, and their accomplishments.