Cahokia Mounds State Historic Site

Cahokia Mounds State Historic Site is an archaeological area near Collinsville, Illinois, on the Mississippi River floodplain. It preserves remnants of an ancient Indigenous city that was the largest urban center in the prehistoric United States north of Mexico, flourishing between approximately 950 and 1350 CE. The site was a primary center of the Middle Mississippian culture and once featured about 120 mounds spread over six square miles. Today, about 70 mounds remain within the historic site, which was designated a UNESCO World Heritage site in 1982.12

The most prominent feature is Monks Mound, the largest prehistoric earthen structure in the Western Hemisphere. Cahokia was a complex society with administrative and ceremonial zones, elite compounds, and residential areas, all oriented to cardinal directions. The city engaged in extensive trade networks, reaching as far as the Gulf of Mexico and the Great Lakes.1

The decline and eventual abandonment of Cahokia, likely around 1350 CE, are attributed to environmental degradation, including deforestation leading to increased flooding and crop failures. This environmental stress may have contributed to societal stress, warfare, and eventual migration of its inhabitants.1