The Cahokia Mounds State Historic Site is the site of a pre-Columbian Native American city (c. 600–1400 CE) directly across the Mississippi River from modern St. Louis, Missouri. This historic park lies in southern Illinois between East St. Louis and Collinsville. The park covers 2,200 acres (890 ha), or about 3.5 square miles (9 km2), and contains about 80 mounds, but the ancient city was much larger. In its heyday, Cahokia covered about 6 square miles (16 km2) and included about 120 human-made earthen mounds in a wide range of sizes, shapes, and functions.
Cahokia Mounds is one of only 22 UNESCO World Heritage Sites, and a U.S. National Historic Landmark.
One of the greatest cities of the world, Cahokia was larger than London was in AD 1250. The Mississippians who lived here were accomplished builders who erected a wide variety of structures from practical homes for everyday living to monumental public works that have maintained their grandeur for centuries.