Overlooking the Muskingum River in Marietta is a complex of earthworks that fascinated the early settlers, because they provided evidence of an earlier people who had once inhabited the land.  These mounds were the first of Ohio's prehistoric Indian earthworks to be accurately surveyed, mapped and described.  When discovered, they were curiosities and much speculation was generated about who built them and what they meant.

We now know that the Conus Mound was built by the Adena Indians (800 B.C. to 100 A.D.).   The square enclosure and other structures were built by the Hopewell Indians (100 B.C. to 500 A.D.)

The directors of the Ohio Company greatly admired these sites and designated them as public places.  Special provisions were made for their protection and preservation, and they remain intact in Marietta today.   These mounds have long been considered to be among the most perfect works of the early mound builders.   Although thousands of these mounds, varying in size and shape, once covered the Midwest, many met with a different fate.  Untold numbers of these mounds were eradicated due to the expansion of farmland and the spreading of settlements.