Native Americans cultivated it in numerous varieties throughout the Americas. The Mississippian culture, whose major city and regional chiefdom of Cahokia in present-day Illinois achieved its peak about 1250 CE, had population density and a great regional trade network based on surplus maize crops. As another example, the women of the Pawnee nation on the Great Plains were known to cultivate ten pure varieties of corn by the late 18th century. After European contact with the Americas in the late 15th and early 16th centuries, explorers and traders carried maize back to Europe and introduced it to other countries through trade. Its use spread to the rest of the world.