Cahokia Mounds

Long before St. Louis existed, a city rose on the floodplain east of the Mississippi. Cahokia was the largest pre-Columbian settlement north of Mexico and the great urban center of the Mississippian world. At its height between about 1050 and 1150, an estimated 10,000 to 20,000 people lived at Cahokia itself, with a much larger population spread across the surrounding region.

The city covered roughly 4,000 acres and once contained about 120 earthen mounds. Some supported important buildings; others served ceremonial or funerary purposes. At the center stood Monks Mound, a four-terraced earthwork about 100 feet high and covering more than five hectares. It remains the largest Indigenous earthen structure north of Mexico. Nearby, circles of wooden posts now called Woodhenge tracked the movement of the sun and reveal how carefully the city was organized around ceremony, time, and landscape.

Cahokia began declining after about 1200 and was largely abandoned by 1400. The reasons remain debated, with scholars examining environmental change, resource pressures, flooding, political transformation, and social upheaval rather than a single simple cause. What survived was the landscape itself: monumental earthworks hiding in plain sight within the modern St. Louis metropolitan area.

Today Cahokia is recognized as a U.S. National Historic Landmark and, since 1982, a UNESCO World Heritage Site. It is not a ruin in the familiar sense of stone walls and temples. Its architecture was built largely from earth and wood. That makes the surviving mounds feel almost deceptively natural—until you climb Monks Mound and realize that the hill beneath your feet was built by human hands, basket by basket, nearly a thousand years ago.