Cahokia was a vast Native American city in southwestern Illinois near the confluence of the Mississippi, Missouri, and Illinois Rivers. Beginning as a settlement around 600 CE, it grew rapidly around 1050 CE into the largest and most influential urban center of the Mississippian world, with an estimated population of 15,000 to 20,000. Its planned plazas, causeways, and earthwork mounds were built through immense labor, and its trade and contact networks reached from the Great Lakes to the Gulf Coast. A political, economic, and ceremonial center, Cahokia declined after upheaval in the late 12th century and was abandoned by about 1350.