The civilization known for the construction of Cahokia mounds in what is now Illinois is the Mississippian culture. Flourishing between 800 and 1600 CE, the Mississippian culture developed complex societies characterized by large, earthen mound construction, extensive trade networks, and agricultural practices that supported large populations. Cahokia, located near present-day St. Louis, was one of the largest urban centers of the period and featured impressive mounds used for ceremonial and political purposes. This civilization was marked by its social stratification, religious practices, and innovations in agriculture, which influenced the future development of Native American societies in North America.