Plum Bayou Mounds: a planned ceremonial centre in the Arkansas valley

The Plum Bayou culture, a regional culture of the Late Woodland period, flourished from about 650 to 1050 on the floodplains of the Arkansas and White rivers and in the neighbouring uplands. Its people lived in farmsteads and small villages, grew native seed plants such as maygrass, little barley, amaranth and chenopodium — maize appears only at late sites and in small amounts — and hunted deer, turkeys and other game, fished and gathered nuts and wild fruit. Exotic materials show contacts with the Ozarks, the Ouachita Mountains and the Coles Creek culture of the lower Mississippi valley.

Their largest centre stood on the bank of an oxbow lake of the Arkansas River. A ditch and an embankment 2.5–3 metres high and some 1.6 kilometres long enclosed it on three sides, the lake closing the fourth. Inside, eighteen mounds, most of them flat-topped platforms for buildings, were arranged around two plazas used for ceremonies and feasts; the two tallest rose about 15 and 12 metres. Only a few religious leaders and their families seem to have lived there. Archaeologists have found that the mounds were placed using a standard unit of about 47.5 metres and that several of them lined up with the rising and setting sun at the solstices and equinoxes.

Between about 900 and 1000 neighbouring peoples adopted maize farming and more complex religious and political institutions, but the Plum Bayou people did not, and their ceremonial centres were abandoned. In the 19th century the site was named after the Toltecs of Mexico, reflecting the mistaken belief that the ancestors of Native Americans could not have built such earthworks; investigations by the Smithsonian’s Edward Palmer in 1883 helped to dispel it. The site became a National Historic Landmark in 1978 and was renamed Plum Bayou Mounds in 2022 after consultation with the Quapaw Nation.