Cahokia Mounds

Cahokia Mounds, group of prehistoric mounds, mostly in the form of truncated pyramids, near East St. Louis, Ill. The largest of these, Monks Mound, is about 1,200 ft (360 m) by 650 ft (200 m) at base and 100 ft (30 m) high, and is the largest mound in the United States. More than 300 of the mounds have in recent years been bulldozed to make way for agricultural and municipal expansion, but the 18 largest remain.