The remains of the most sophisticated prehistoric native civilization north of Mexico are preserved at Cahokia Mounds State Historic Site. Within the 2,200-acre tract, located a few miles west of Collinsville, Illinois, lie the archaeological remnants of the central section of the ancient settlement that is today known as Cahokia.

View of Monk's Mound

A World Treasure
In 1982, the United Nations Educational, Scientific, and Cultural Organization (UNESCO), designated Cahokia Mounds a World Heritage Site for its importance to our understanding of the prehistory of North America. Cahokia Mounds has also been recognized as a U. S. National Historic Landmark. Cahokia Mounds is managed by the Illinois Historic Preservation Agency as a State Historic Site.

A Thriving Ancient Metropolis
According to archaeological finds, the city of Cahokia was inhabited from about A.D. 700 to 1400. At its peak, from A.D. 1050 to 1200, the city covered nearly six square miles and 10,000 to 20,000 people lived here. Over 120 mounds were built over time, and most of the mounds were enlarged several times. Houses were arranged in rows and around open plazas, and vast agricultural fields lay outside the city.

The site is named for the Cahokia subtribe of the Illiniwek (or Illinois tribe, a loose confederacy of related peoples), who moved into the area in the 1600s. They were living nearby when the French arrived about 1699. Sometime in the mid-1800s, local historians suggested the site be called "Cahokia" to honor these later arrivals.

Archaeological investigations and scientific tests, mostly since the 1920s and especially since the 1960s, have provided what is known of the once-thriving community.

The Mystery of Cahokia
The fate of the prehistoric Cahokians and their city is unknown, but the decline seems to have been gradual, beginning around the 1200s. By A.D. 1400 the site had been abandoned. Exactly where the people went or what tribes they became is yet to be determined.

Depletion of resources probably contributed to the city's decline. Climate change after A.D. 1200 may have affected crop production and the plant and animal resources needed to sustain a large population. War, disease, social unrest, and declining political and economic power may have also taken their toll.