The area called the American Bottom stretches 70 miles in Illinois from Alton to Chester. The wide and fertile flood plain is the product of the merging of three big rivers: the Missouri, Mississippi, and Illinois. It’s no wonder why the area has attracted settlers for at least 12,000 years.
Paleo-Indians hunted and lived in the area, probably for centuries. Indians in the Woodlands era flourished along the Ohio River and up the Mississippi. They built thousands of mounds, cultivated crops, developed the bow and arrow and the flint hoe, and influenced centuries of religious practices.
The climate in the region warmed around 1,200 years ago and stayed more temperate and wetter for four centuries. These changes improved conditions for agriculture, which may have contributed to the rapid growth of Mississippian culture.