Cahokia Mounds State Historic Site

The Cahokia Mounds State Historic Site is located directly across the Mississippi River from modern St. Louis, Missouri. It is the site of a pre-Columbian Native American city dating back to c.600-1400 CE.

This Native American historic park lies in southern Illinois between East St. Louis and Collinsville.  The park consists of 2,200 acres or about 3.5 square miles in size.  This site contains approximately 80 mounds; however, in ancient times, the city was much larger.  At its peak, Cahokia Mounds covered almost 6 square miles and included about 120 man-made earthen mounds in a large assortment of sizes, shapes, and functions.

Cahokia Mounds has a unique and important distinction as the largest and most complex archaeological site north of the pre-Columbian cities of Mexico.

Cahokia Mounds is state-protected and a registered National Historic Landmark.  It is also one of only 23 UNESCO World Heritage Sites within the United States.  As the largest prehistoric earthen construction site north of Mexico, the site is open to the public, maintained by the Illinois Historic Preservation Division, and supported by the Cahokia Mounds Museum Society.

History the Cahokia Mounds State Historic Site

Cahokia was the largest and most important urban settlement of the Mississippian culture.  Advanced societies developed across much of what is now the central and southeastern United States, beginning more than 1,000 years before European contact.  Their settlements ranged across the Midwest, Eastern, and Southeastern United States.

One of the major problems that likely plagued Cahokia was keeping a steady supply of food.  Another problem was waste disposal for the dense population, and Cahokia became unhealthy from polluted waterways.  Because it was such an unhealthy place to live, it is believed that the town had to rely on social and political attractions to bring in a steady supply of new immigrants; otherwise, the town’s death rate would have caused it to be abandoned earlier.

The population of Cahokia began to decline during the thirteenth century, and the site was eventually abandoned around 1300.  Scholars have surmised that environmental factors, such as overhunting, deforestation, and flooding, as explanations for the abandonment of the site.

Another possible theory is invasion by outside peoples, though the only evidence of warfare found thus far is the defensive wooden stockade and watchtowers that enclosed Cahokia’s main ceremonial precinct.  Since no other proof of warfare was found, the palisade may have been more for ritual or formal separation than for military purposes. Finally, diseases transmitted among the large, dense urban population are another possible cause of decline and abandonment.

In 2015, researchers found evidence of major floods at Cahokia, severe enough to flood dwelling places.  Analysis of sediment from below Horseshoe Lake has revealed that two major floods occurred in the settlement period at Cahokia, in roughly 1100-1260 and 1340-1460.


The Cahokia Museum and Interpretive Center receive up to one million visitors per year.  The building opened in 1989 and has received the Thomas H. Madigan Award, the St. Louis Construction News & Reviews Readers Choice Award, the Merit Award from the Metal Construction Association, and the Outstanding Achievement Award from the Brick Manufacturer Association.