Archaeological evidence shows that an earthen mound burial culture existed in the Piedmont from 950 AD to the time of European contact. It spanned the so-called Late Woodland Period. These burial mounds, some of them reaching heights of at least , are believed to have been made by the ancestors of the Manahoac and other eastern Siouan groups. They are unique in that they contained hundreds to thousands of corpses. They are sometimes called "accretional mounds". The people added more soil to them as additional individuals were buried within. Most of the burial mounds have been either completely destroyed by plowing or significantly reduced in size by erosion and flooding.