Aztalan was first settled around 900 CE by a Native American culture known as the Middle Mississippian Tradition. The chief center of a Middle Mississippian settlement is at Cahokia, in present-day Illinois, a city that at its peak had 20,000–30,000 people. This was not surpassed by Europeans in North America until after 1800. These settlements are characterized by the construction of earthwork mounds, stockades, and houses, by decorated Mississippian culture pottery, and agricultural practices. There are also elements of the Woodland culture found there.