the development of pottery and the small-scale horticulture of the Eastern Agricultural Complex. 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. Trade with the Northeast indigenous peoples via the Ohio River began during the Burial Mound Period (1000 BC–AD 700) and continued until European contact. The agrarian Mississippian culture covered most of the state from 1000 to 1600 AD, with one of its major centers being at the Moundville Archaeological Site in Moundville, Alabama, the second-largest complex of this period in the United States. Some 29 earthwork mounds survive at this site. Analysis of artifacts recovered from archaeological excavations at Moundville were the basis of scholars' formulating the characteristics of the Southeastern Ceremonial Complex (SECC). Contrary to popular belief, the SECC appears to have no direct links to Mesoamerican culture, but developed independently. The Ceremonial Complex represents a major component of the religion of the Mississippian peoples; it is one of the primary means by which their religion is understood. The early historic Muscogee are considered likely descendants of the Mississippian culture along the Tennessee River in modern Tennessee, Georgia and Alabama. They may have been related to the Utinahica of southern Georgia. At the time the Spanish made their first forays inland from the shores of the Gulf of Mexico, many political centers of the Mississippians were already in decline, or abandoned. Among the historical tribes of Native American people living in the area of present-day Alabama at the time of European contact were the Muskogean-speaking Alabama (Alibamu), Chickasaw, Choctaw, Creek, Koasati, and Mobile peoples. Also in the region were the Iroquoian-speaking Cherokee, from a different family and cultural group. They are believed to have migrated south at an earlier time from the Great Lakes area, based on their language's similarity