Before European settlement, the area was home to indigenous peoples for many centuries. The peak civilization was created by peoples of the Mississippian culture, known as the Mound Builders. With the cultivation of maize, they were able to create food surpluses and build concentrated settlements in the centuries after 600 CE. The Cahokia Mounds Site, which was built as the center attracted a rapid increase in population after 1000 CE, is a six-square mile complex of large, man-made, earthen mounds rising from the flood plain. In 1982, it was designated by UNESCO as one of only eight World Heritage Sites in the United States.