Mound Builders
The mound builders of the Ohio River Valley and the Mississippian culture of the lower Midwest did sustain some large settlements after the incorporation of corn planting into their way of life during the first millennium AD. The Mississippian settlement at Cohokia, near present-day East St. Louis, Ill., was perhaps home to 40,000 people in about AD 1100. But mysteriously, around the year 1300, both the Mound Builder and the Mississippian cultures had fallen to decline.

