Many have studied the series of earthworks left behind by the Hopewell and Adena moundbuilders who lived in the region some 2,000 years ago. However, the relatively few who have studied the mounds cannot agree on their purpose.
“There aren’t too many people around who know very much about the mounds,” said John Briley, former manager of the Ohio River and Campus Martius museums. “And that’s too bad because they are very interesting works.”
When the first military and civilian settlers arrived in what is now Marietta, they found groups of earthworks that extended over 95 acres.
Unfortunately, many of the Marietta mounds were carelessly destroyed in the last 200 years. Many mounds in other Ohio cities met similar fates.
One example of this careless destruction came in , when two massive mounds that lined Sacra Via were sold by Marietta City Council to a local businessman. The earth from the mounds was made into bricks and used in the construction of many downtown buildings, including the First Unitarian Universalist Church on Putnam Street.
Fortunately, before most of the mounds were destroyed Charles Whittlesey, a topographical engineer for the state of Ohio detailed the location, shape and height of the Marietta mounds in 1837.
It allows today’s archaeologists and historians to theorize about the purpose of the mounds.
The Native Americans who were living in Ohio at the time it was settled were from other tribes — primarily Cheyenne in this region — and possessed no knowledge or understanding of the mounds. Exactly what happened to the moundbuilders themselves also remains a mystery.
Early settler theories about the Marietta earthworks thought of them as structures built for worship, burials or defense. Those thoughts were generally accepted for many years, and to some degree may still hold merit.
More recent theories are the product of extensive studies of mound sites from across the region that suggest the Hopewell and Adena tribes were members of a complex society that used mounds for astronomical charting and recording.
According to theorists, many mound sites in the region were arranged to help identify key dates, such as solstices and equinoxes.
An example, according to the theory, is that the Marietta winter sunset is marked at an angle of 239 degrees from true north. That is the angle of a straight line from the top of mound Conus in Mound Cemetery to the southernmost stone mound on Harmar Hill. Other lines can be made to identify the rise of prominent stars and constellations.
It would mean Conus was basically used as a giant sundial.
It is one of many possible theories, said archaeologist Wes Clarke, of Marietta.
“That is one possible theory,” Clarke said. “But you can take a map like that and make lines pointing in every direction and still not know what you’ve got.
“We still aren’t sure what the mounds’ real purpose was.”
Clarke said most conclude after studies of earthworks similar to Marietta’s holds that the mounds operated as ceremonial centers which were visited periodically by the natives.
Conus in Mound Cemetery, circa 1898