The Cahokia Mounds are all that remains of the largest pre-Columbian settlement north of Mexico. At its peak it is estimated up to 20,000 people lived here. It was the largest known city to have existed in the United States until Philadelphia topped that population in the late 18th century. It was the epicenter of Mississippian culture, with its influence extending through much of the southeastern United States. Peoples from many different Native tribes lived together here during the Mississippian period (800-1350).
80 of the original 120 mounds remain today. The largest of these is known as Monks Mound, which covers 14 acres and is 100 feet high. Mounds served different purposes in Cahokian society. One of the burial mounds (Mound 72) was excavated from 1967-1971. The remains found there have helped piece together some of the mystery of this ancient civilization.