Two groups occupied the site in prehistoric times. The Siouan-speaking Middle Missouri people (Initial Middle Missouri variant), ancestral to the historic Mandan people, first occupied the site sometime after about 900 AD. They built numerous earth lodges on the lower portion of the site. Caddoan-speaking Central Plains people (Initial Coalescent variant) moved into the area from southern areas (present-day Nebraska) sometime around 1150 AD. (The historic Arikara are a Caddoan people.) Whether they displaced the earlier group or moved on to an abandoned site is unknown. The Central Plains (Initial Coalescent) people built at least 55 lodges, mostly on the upper part of the site. There is no direct evidence that there was conflict between the two groups, and scholars have found evidence that both cultures changed gradually in relation to the other.