The Serpent Mound sprawls across a broad plateau overlooking Ohio Brush Creek in Adams County. Though it’s one of the most iconic monuments of ancient America, archaeologists still don’t agree about which of Ohio’s early American Indian cultures built it.
One reason for the difficulty in sorting out what would seem to be a simple question is that this plateau was a busy place in antiquity.
When Frederic Putnam of Harvard University’s Peabody Museum investigated the site back in the 1880s, he found evidence that the plateau had been occupied during three main periods.
At around 450 B.C., the Adena culture built two burial mounds there next to a small habitation area. About a thousand years later, the so-called Intrusive Mound culture added several burial sites to the largest Adena mound, but left behind little else to indicate they’d been there. At around A.D. 1100, the Fort Ancient culture had a village at the site that must have been occupied for a number of years. It appears to have included about 20 houses surrounded by a palisade with a small burial mound not far off.
In 2011, ASC Group Inc. conducted an archaeological investigation at Serpent Mound on behalf of the Ohio History Connection. The restrooms at the site were being renovated, which required the installation of new utility lines. The ASC team excavated 81 test units and six test trenches along the proposed path of the utility lines to make sure the construction work didn’t inadvertently damage any important archaeological evidence.
Kevin Schwarz, the archaeologist in charge of the project, shares what they found in a paper recently published in a special issue of the Journal of Ohio Archaeology devoted to the Serpent Mound.
Much of the work was concentrated where the utility lines were going to come closest to the large Adena burial mound, which Putnam had excavated and restored back in the 1880s. Schwarz and his team recovered 195 prehistoric artifacts, including an Adena spear point and several fragments of Fort Ancient pottery.
The most interesting discoveries, however, were a shallow basin uncovered in a test pit and an ancient ground surface, buried at some point in the past by another layer of earth, exposed in a test trench. Radiocarbon dates on charcoal from the features established that the basin was used by the Adena culture between about 500 and 400 B.C., whereas the buried ground surface was used by the Fort Ancient culture between about A.D. 1000 and 1200.
Schwarz acknowledges that the ASC investigation didn’t uncover any direct evidence for the age of Serpent Mound, but he does note that the radiocarbon date for the buried soil surface closely matches radiocarbon dates on charcoal from the Serpent Mound obtained by a team of researchers with whom I worked back in the 1990s.
The correspondence between those dates is consistent with the hypothesis that the Fort Ancient villagers built Serpent Mound, but it’s by no means a “smoking gun.”
As Schwarz makes clear, because all of those different cultures lived on the Serpent Mound plateau, “it will take a lot of careful attention” to the contexts of artifacts, features and charcoal samples “to determine with certainty” the age of the Serpent Mound.
Brad Lepper is a curator of archaeology at the Ohio History Connection.