Cahokia Mounds State Historic Site, located between East St. Louis and Collinsville in southwestern Illinois, is the site of an ancient Native American city which was active from around 1050 to 1350 CE. The park is spread across 2,200 acres, containing 80 manmade mounds and encompassing 6 square miles at its peak. These earthworks come in a variety of sizes and shapes, each serving different functions.