Southern United States that marks a significant change in the cultural history of the area. Population and cultural and political complexity increased, especially by the end of the Coles Creek period. Although many of the classic traits of chiefdom societies had not yet developed, by 1000 CE, the formation of simple elite polities had begun. Coles Creek sites are found in Arkansas, Louisiana, Oklahoma, Mississippi, and Texas. The Coles Creek culture is considered ancestral to the Plaquemine culture. Mississippian cultures Around 900–1450 CE, the Mississippian culture developed and spread through the Eastern United States, primarily along the river valleys. The largest regional center where the Mississippian culture is first definitely developed is located in Illinois along a tributary of the Mississippi, and is referred to as Cahokia. It had several regional variants including the Middle Mississippian culture of Cahokia, the South Appalachian Mississippian variant at Moundville and Etowah, the Plaquemine Mississippian variant in south Louisiana and Mississippi, and the Caddoan Mississippian culture of northwestern Louisiana, eastern Texas, and southwestern Arkansas. Like the mound builders of the Ohio, these peoples built gigantic mounds as burial and ceremonial places. Fort Ancient culture Fort Ancient is the name for a Native American culture that flourished from 1000 to 1650 CE among a people who predominantly inhabited land along the Ohio River in areas of modern-day southern Ohio, northern Kentucky, and western West Virginia. Plaquemine culture A continuation of the Coles Creek culture in the lower Mississippi River Valley in western Mississippi and eastern Louisiana. Examples include the Medora site in West Baton Rouge Parish, Louisiana; and the Anna and Emerald Mound sites in Mississippi. Sites inhabited by Plaquemine peoples continued to be used as vacant ceremonial centers without large village areas much as their Coles Creek ancestors had done, although their layout began to show influences from Middle Mississippian peoples to the north. The Winterville and Holly Bluff (Lake George) sites in western Mississippi are good examples that exemplify this change of layout, but continuation of site usage. During the Terminal Coles Creek period (1150 to 1250 CE), contact increased with Mississippian cultures centered upriver near the future St. Louis, Missouri. This resulted in the adaption of new pottery techniques, as well as new ceremonial objects and possibly new social patterns during the Plaquemine period. As more Mississippian culture influences were absorbed, the Plaquemine area as a distinct culture began to shrink after