Great Serpent Mound
North America's largest serpent-shaped earthwork stretches a quarter mile along an Ohio ridge. Archaeologists have argued for over a century about which ancient culture built it, and when. A 1991 radiocarbon study pointed to the Fort Ancient culture; a 2014 study revived the older Adena attribution.
Field Guide Entry
Overlooking Ohio Brush Creek in Adams County, the Great Serpent Mound is a quarter-mile-long effigy of a curving snake, built from packed earth onto a high plateau, with a triangular head aligned toward the setting sun on the summer solstice. American antiquarians Ephraim Squier and Edwin Davis surveyed and published the first detailed account of the mound in 1848, helping spark the broader 19th-century fascination with the Ohio Valley's earthworks. Frederic Ward Putnam excavated the site in the 1880s and led the campaign that purchased and preserved it as one of America's first archaeological parks.
For decades, archaeologists credited the Adena culture (roughly 800 BCE to 100 CE) with the mound's construction, based on Adena burial mounds found nearby. A 1991 excavation using radiocarbon dating instead pointed to the Fort Ancient culture, active centuries later between 1000 and 1500 CE, which is also known to have carved serpent imagery into other artifacts. A 2014 study revived the Adena attribution using newer sediment-dating techniques, only for critics to challenge the sample quality. The most recent Bayesian statistical analysis of multiple radiocarbon samples suggests a middle path: the mound may have been built by the Adena around 2,300 years ago, then substantially rebuilt by the Fort Ancient people some 1,400 years later.
The dating dispute isn't a fringe theory versus mainstream science story. It's a disagreement between credentialed archaeologists working from the same physical evidence, complicated by the fact that earthen mounds don't preserve datable organic material as cleanly as stone or ceramic artifacts. Even the multistage theory remains one interpretation among several. Who shaped Serpent Mound's curves, and was the head's alignment with the solstice sunset deliberate astronomy or coincidence?
Visiting Information
Open Tuesday through Saturday, 10am to 5pm, and Sunday noon to 5pm; closed Mondays. Admission is $8 per vehicle. The Ohio History Connection operates a small museum, observation tower, and walking trail around the mound.
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