Cahokia Mounds is the largest pre-Columbian settlement north of Mexico. This agricultural society may have had a population of 10,000-20,000 at its peak between 1050 and 1150, which was equivalent to the population of many European cities at that time. It was occupied primarily during the Mississippian period (800-1400), when it covered nearly 1,600 hectares and included some 120 mounds. It is a striking example of a complex chiefdom society, with many satellite mound centres and numerous outlying hamlets and villages. Primary features at the site include Monks Mound, the largest prehistoric earthwork in the Americas.