The Fort Ancient culture was a significant Native American archaeological group that flourished in the Ohio River valley from approximately 1000 to 1750 CE, existing as a distinct "sister culture" to the Mississippian people. They are notably credited with introducing maize agriculture to Ohio and constructing well-organized villages with central plazas that likely functioned as solar calendars.
This culture is linked to impressive ceremonial effigy mounds, including the Great Serpent Mound and the Alligator Effigy Mound, which archaeological studies, such as one by Brad Lepper and Tod A. Frolking in 1999, have re-dated to the Fort Ancient era and re-interpreted as ceremonial sites rather than burials. Over time, their settlements evolved from small, scattered groups into larger, fortified villages by the Late Fort Ancient period (1400-1750 CE), a time that saw populations coalesce and an apparent increase in warfare, leading to defensive palisades. Despite its name, the iconic Fort Ancient earthworks were originally built by the older Hopewell culture and served as a ceremonial site, not a fortress, only later occupied by the Fort Ancient people.