Atwater was recognized by contemporaries as a pioneer of the study of the mounds or massive earthworks in the Ohio Valley; he published an account during 1820. These are now known to have been constructed by ancient Native Americans of the United States. At the time, Atwater and other scholars developed various theories of origin; he thought a culture other than ancestors of Native Americans created such monuments. He helped publicize a theory by John D. Clifford, an amateur of Lexington, Kentucky, who suggested that people related to Hindus of India had migrated by sea and built the mounds, to be replaced by ancestors of contemporary Native Americans.
