The Cahokia Mounds State Historic Site is the site of a pre-Columbian Native American city directly across the Mississippi River from modern St. Louis, Missouri. This historic park lies in south-western 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. At its apex around 1100 CE, the city covered about 6 square miles (16 km2) and included about 120 manmade earthen mounds in a wide range of sizes, shapes, and functions. At the apex of its population, Cahokia may have briefly exceeded contemporaneous London, which at that time was approximately 14,000–18,000.
