The Hopewell people built Mound 7, the Central Mound and largest of the Mound City Group, with carefully sequenced layers rather than simply piling up dirt. Over a large central grave, they first placed mounded clay capped with sand, then added three more clay layers topped with sand at 1-foot intervals, and finished with several more feet of clay covered by 20 inches of gravel. This enormous effort was part of a broader construction program that also included 23 other mounds and a surrounding earthen wall, a cumulative process that may have taken decades or centuries and required significant coordination of labor. Thirteen cremated burials were uncovered in the mound, along with many copper objects made from material mined 600 miles away near Lake Superior. Central Mound survived destruction when Henry Shetrone of the Ohio State Archaeological and Historical Society helped stop the Army from removing it, and Camp Sherman workers built around it so William Mills could study it archaeologically in the 1920s.