Mandan (mănˈdăn, –dən) [key], indigenous people of North America whose language belongs to the Siouan branch of the Hokan-Siouan linguistic stock (see Native American languages). The Mandan were a sedentary tribe of the Plains area and were culturally connected with their neighbors on the Missouri River, the Arikara and the Hidatsa. The Mandan had certain distinctive cultural traits, which included a myth of origin in which their ancestors climbed from beneath the earth on the roots of a grapevine. According to tradition, at one time the Mandan lived to the east, but their movements in historic times were westward up the Missouri River. By the mid-18th cent., they lived in nine villages near the mouth of the Heart River in S central North Dakota. After having suffered severely from smallpox and the attacks of the Assiniboin and the Sioux, the Mandan moved farther up the Missouri River to a point opposite the Arikara villages. Here the Mandan survivors merged into two villages on opposite sides of the Knife River. They were visited (1804) by Lewis and Clark, who said that they numbered some 1,250. In 1837, after an epidemic of smallpox and cholera, the Mandan were reduced to some 150, all dwelling in a single village. When the Hidatsa moved (1845) from the Knife River region N to the Fort Berthold trading post, the few Mandan joined them. A large reservation was set aside (1870) for the Mandan, the Hidatsa, and the Arikara in North Dakota (Fort Berthold Reservation). There were some 1,200 Mandan in the United States in 1990.
See G. Catlin, O-Kee-Pa, a Religious Ceremony, and Other Customs of the Mandans (1867, centennial ed. by J. C. Ewers, 1967).