Prehistoric Native American groups such as Adena, Hopewell, and Fort Ancient built mounds in the Midwest that can still be seen today. These mounds were used for a variety of purposes, including burial, ceremonial, and residential purposes. Some of the most well-known mounds in the Midwest include the Serpent Mound in Ohio, the Cahokia Mounds in Illinois, and the Great Serpent Mound in Ohio.