The Mississippian culture arose as the cultivation of Mesoamerican crops of corn and beans led to crop surpluses and population growth. Increased population density gave rise of urban centers and regional chiefdoms, of which the greatest was the city known as Cahokia, in present-day Illinois near the confluence of the Illinois and Mississippi rivers. The culture spread along the Ohio and Mississippi rivers and their tributaries. Its population of 20,000 to 30,000 at its peak exceeded that of any of the later European cities in North America until 1800. Stratified societies developed, with hereditary religious and political elites, and flourished in what is now the Midwestern, Eastern, and Southeastern United States from 800 to 1500 C.E.