Throughout most of the nineteenth century, it was believed that the tens of thousands of earthen mounds that dotted the central United States were engineering feats created by a mysterious, lost race - a race that had been destroyed by the less civilized Indians. By the late 1880s, it was becoming clear that the mounds were actually built by ancestors of the numerous native American groups that still inhabited the central states, such as the Natchez. This film reconstructs the history of ideas associated with the mounds and their builders, from the mid-nineteenth century explorations of curious citizens, to contemporary archaeological research in the Illinois River Valley.