Mandan bone chipping tools, used to create stone (flaking flint) implements. Mandan village site, North Dakota. The Mandan historically lived along the banks of the Missouri River and two of its tributaries in present-day North and South Dakota. Speakers of Mandan, a Siouan language, developed a settled, agrarian culture. They established permanent villages featuring large, round, earth lodges, some 40 feet (12 m) in diameter, surrounding a central plaza. While the bison was key to the daily life of the Mandan, they also farmed and actively traded goods with other Great Plains tribes. Ethnologists and scholars studying the Mandan subscribe to the theory that, like other Siouan-speaking people, they originated in the area of the mid-Mississippi River and the Ohio River valleys in present-day Ohio. A migration is believed to have occurred possibly as early as the 7th century but probably between 1000 CE and the 13th century, after the cultivation of maize was adopted.