Cahokia was the largest prehistoric Indian community in America north of Mexico. It covered an area of six square-miles, including at least 120 mounds of different size and function. Initial occupation during Late Woodland times (AD 700-800) included small settlements along Cahokia Creek. These expanded and merged during early Mississippian times (AD 800-1000), and the population and community increased, reaching a peak between AD 1050-1150 with an estimated population of 10-20,000. A period of change and population decline began in the 1200s, and by AD 1350-1400, Cahokia had been abandoned. Indians of the Mississippian culture built this community and many other large and small ones throughout the Mississippi floodplain and the adjacent uplands. Cahokia was the center of a large complex chiefdom that had ceremonial and trade connections to other Mississippian sites throughout the Midwest and Southeast. Long-distance trade brought many exotic materials to Cahokia, including Gulf Coast and Atlantic sea shells, copper from around Lake Superior, mica from the southern Appalachians, and chert, salt, minerals, and other goods from throughout the Midwest. The decline of Cahokia may be attributed to a combination of many factors, including depletion of resources in the region; internal social and political unrest; external friction and conflicts with other groups; climatic changes affecting crops and local flora and fauna; soil exhaustion due to intensive agriculture; and loss of control and influence over contemporary sites and groups.