THE SERPENT MOUND DEBATE

Archaeologists disagree about who built this remarkable effigy mound, and when they did it.

By David Malakoff

Anyone who has tried to catch a snake knows the reptiles are elusive. So it only seems appropriate that Serpent Mound, a twisting, quartermile long, three-foot-high earthwork in southern Ohio, has eluded archaeologists’ grasps for decades. Over the past 170 years, researchers have offered changing and conflicting views on the age of the iconic effigy, which has been designated a National Historic Landmark. Some believe that people of the Adena culture, who created countless elaborate earthen mounds in the central Ohio River Valley and adjacent lands, built the serpent about 2,300 years ago. But others assert that it’s

An aerial photograph of Serpent Mound taken from a drone. The mound is a National Historic Landmark.

less than half that age, and that it was produced by the Fort Ancient people, who also built earthworks in this region.

Regardless of who is right, recent research has cast new light on one of North America’s most distinctive, mysterious, and disputed ancient sites. “The great Serpent Mound is a really special place,” said archaeologist Bradley Lepper of the nonprofit Ohio History Connection, which owns the site. “You can’t walk along those curves without wanting to know more about who built it, when they built it, and what they were thinking. It is just a fascinating effigy.”

In the 1840s, journalist Ephraim Squier and physician Edwin Davis—both avid artifact collectors—embarked on a systematic effort to document and map ancient earthworks across the Eastern United States. In 1846, acting on a vague tip about a “work of defence” atop a heavily wooded cliff overlooking Brush Creek in Adams County, the two men were surprised to find the giant effigy. After careful mapping (a backbreaking task), its form became clear: an enormous

Jarrod Burks runs a ground-penetrating radar machine over the mound, looking for evidence of nineteenth-century excavation trenches and details of the Serpent’s construction.

egg-shaped head with a single eye, attached to a body with a half-dozen curves and a tightly coiled tail. It was, they later wrote, “probably the most extraordinary earthwork thus far discovered.”

Scholarly speculation about the serpent’s origins began swirling. Squier and Davis wondered if it was somehow linked to Egyptian, Greek, Celtic, or even Chinese cultures, since the serpent and the “circle, egg, or globe has been a predominant symbol among many primitive nations.” In the 1880s, however, other investigators challenged that idea, suggesting the serpent was likely a homegrown invention, not a foreign import. It wasn’t until 1887, however, that Frederic Putnam of Harvard University’s Peabody Museum launched a systematic dig. For three field seasons, his team excavated the head and body of the serpent—which had already been damaged by erosion, vandalism, and farming activities—and also explored adjacent burial mounds, graves, and apparent occupation sites. They found no major artifacts in the serpent itself, but they did find numerous items within two stratigraphic layers of soil at surrounding sites; they suggested that prehistoric people had occupied the area during at least two periods, one older than the other.

Putnam believed the serpent’s builders were associated with the older occupation. It wasn’t until the 1930s and ‘40s, however, that researchers began formally classifying and dating the artifacts that Putnam’s team had recovered. They determined that many of the items from the younger occupation were associated with the Fort Ancient culture, which lasted from about A.D. 1000 to 1650. Artifacts from the older occupation, including those from a large conical burial mound about 600 feet southeast of the serpent, were associated with the Adena culture, which existed in the upper Midwest from about 500 B.C. to A.D. 100. By the 1940s, the serpent’s close proximity to the conical Adena burial mound and many of the artifacts, together with the perception that the snake was a common Adena artistic motif, had persuaded a number of researchers that the Adena built the mound.

By the time this idea became conventional wisdom, Serpent Mound, which Putnam had rebuilt in the 1890s, had become the centerpiece of a public park. Numerous visitors came to gawk at it and speculate about its origins and purpose. Then, a century after the Serpent was reconstructed,

two avocational archaeologists, Robert Fletcher and Terry Cameron, helped catalyze a new study that challenged the conclusion that the Adena built the mound. Fletcher and Cameron were interested in investigating the idea that the serpent might be a kind of seasonal timekeeper aligned with the movements of the sun, moon, or planets. But to test their ideas, they needed a highly accurate topographic map of the serpent, which didn’t exist. For help, they contacted Lepper and other professional archaeologists, who saw this as an opportunity for a broad new investigation of the serpent.

Radiocarbon testing, which didn’t exist in Putnam’s day, allows archaeologists to date tiny samples of charcoal. Putnam had reported finding an ashy layer of soil at the base of the serpent, and Lepper and his colleagues assumed the ashy layer resulted from the burning of vegetation prior to the mound’s construction. “And we realized that if we could date that ash, we’d know when construction began,” said Lepper, who led the investigation.

In 1991, the team began the first major excavation of the mound since Putnam’s work, taking soil cores and reopening what they believed to be one of the original excavations. They were disappointed, however, to find no trace of the ashy layer he had described. Still, they did recover two small chunks of burned oak from deep within the mound, but above the foundational soil. Both pieces of charcoal were radiocarbon dated to approximately 900 years ago. “That pointed to a Fort Ancient age—not Adena,” Lepper said.

The reexamination also turned up other hints that the serpent was about 900 years old, the researchers reported in a 1996 paper in the Midcontinental Journal of Archaeology. When Lepper and other Ohio History Connection archaeologists dug trenches to install some new waterlines, for example, they revealed fresh evidence, including stone and ceramic artifacts, of a relatively large Fort Ancient occupation just 300 feet south of the serpent. (Putnam had also described this occupation, which he believed to be a village.) And when the researchers examined the notion that the snake was a notable motif in Adena art or earthworks, they concluded it wasn’t: “Very few serpent motifs have been recovered from Adena” sites, they wrote. But by Fort Ancient times serpent motifs “bearing much artistic resemblance to Serpent Mound become widespread in the archaeological record.” Taken together, the authors wrote, the evidence suggested that “the conventional interpretation of Serpent

These copper serpent pendants were recovered from Madisonville, a Fort Ancient site in southwest Ohio. Bradley Lepper and his colleagues argue that this is evidence of a connection between the Fort Ancient people and Serpent Mound.

Mound as Adena rests on a somewhat tenuous foundation.”

Twenty years later, however, the Adena scenario received more support. In 2011, a multidisciplinary team from a number of organizations began another investigation called the Serpent Mound Project. They employed LiDAR to create a fine-grained map of the serpent’s surface, magnetic sensors to search for buried features such as old trenches and hearths, and coring machines that removed eighteen soil samples out of different parts and depths of the mound. The results, published in 2014 in the Journal of Archaeological Science, included some surprises. Near the serpent’s head, for instance, the magnetic sensors detected soil that had formed a previously unknown curve on the east side of the serpent’s neck. “We call it the stealth, or lost, coil,” said Jarrod Burks of the consulting firm Ohio Valley Archaeology, which led the magnetic mapping effort. “It doesn’t seem to fit with the head we see today, and it looks like it was erased before the current design was built.”

The bigger news, however, was the radiocarbon dates that the team got from charcoal and other organic material in four soil samples that appeared to come from the ancient surface on which the serpent was built. They produced dates ranging from 639 to 303 B.C., with a midpoint at 321 B.C.“That puts construction squarely in the Adena period” about 2,300 years ago, said archaeologist William Romain, who directed the project.

But that doesn’t mean the 900-year-old dates reported in the 1996 study are wrong, according to Romain. Instead, those dates suggest the serpent has a long and complicated history, likely marked by multiple periods of use, abandonment, repair, and modification. One plausible scenario, he said, is that the Adena built the serpent, later people modified it (erasing the coil for instance), and Fort Ancient people undertook major repairs of the eroded coils, introducing charcoal from their time period into the structure. “Based on all the lines of evidence, that’s one of the best options,” Romain said.

This year, he and his allies doubled down on that view in a paper scheduled for publication in the Midcontinental Journal of Archaeology that suggests exactly which of the serpent’s coils might have been eroded and then repaired long after it was built. The study also challenges the idea that a lack of serpent imagery at Adena sites suggests the mound was a Fort Ancient product. “There are many reasons why people or creatures may or may not be represented in prehistoric imagery,” the authors wrote. “We do not find images of Buddha, Muhammad, or Jesus made during their lifetimes; but that does not mean they were not important.” The bottom line, said Romain, “is that you can’t give the [Fort Ancient] date an edge based on iconography.”

Lepper, for one, isn’t convinced by this argument. One potential problem with the Serpent Mound Project’s conclusions, he said, is that the researchers can’t be sure their 2,300-year-old radiocarbon dates come from the surface on which the mound was originally built. That’s because, if Putnam was right, the builders scraped away all the topsoil

The previously unknown lost coil is seen in this image of the magnetic survey data.

prior to construction. So the archaeologists might have dated older soil that sits below that surface, skewing the analysis. “All you can really say for sure is that it was built sometime after about 300 B.C., but it doesn’t tell you how long after,” said Lepper. “All the old topsoil that would tell you may be gone.”

Lepper and his colleagues argue that Serpent Mound bears a close resemblance to Fort Ancient-era carvings, jewelry, and pictographs involving snakes, especially images from Picture Cave, a Mississippian site in eastern Missouri, that appear to tell an origin story involving a snake. (The Fort Ancient adopted Mississippian iconography and beliefs, according to Lepper.) “We believe the imagery in Picture Cave and Serpent Mound are telling the same epic story,” they wrote in a paper they hope to publish in a peer-reviewed journal.

Lepper and his colleagues also ask why the effigy is so different from the many other earthworks that have been credited to the Adena, few of which appear to depict animals. “If Serpent Mound was created by the Adena culture, then it existed in a splendid isolation that persisted for nearly a thousand years before anything else like it appeared,” they wrote. “If, on the other hand, it was created by the Fort Ancient culture, then it has a clear cultural context.”

At the same time, Lepper conceded that the radiocarbon dates that loom large in his argument for the Fort Ancient could be a problem. The 900-year-old charcoal could have been transported to the mound long after it was built—possibly by nature, or perhaps by Fort Ancient repair crews, or the workers who centuries later rebuilt and maintained the serpent. The Fort Ancient charcoal “is a strong piece of evidence,” he said, “but not a definitive piece.”

It may be that the only way to resolve this debate is by collecting more and better data. “Both sides have strong and weak points,” said David Pollack, the director of the Kentucky Archaeological Survey. “I think the verdict is still out. There are a lot of questions.” It’s possible dating more charcoal samples might provide a resolution, or better yet, finding dateable artifacts that are within the mound itself or “clearly in a context related to the building of the mound,” he said. But, so far more than a century of digging has failed to uncover such diagnostic artifacts.

The archaeologists agree that a relatively new dating technique called optically stimulated luminescence—which measures how long it has been since sand grains were exposed to sunlight—could be a powerful tool for dating both the foundational surface and the matrix of the mound. But conducting such studies will require more funding as well as the required permits to once again trench or core the mound. So it could be a lengthy wait.

In the meantime, the researchers continue to try to come to grips with the serpent. “We know there’s a lot more to learn out there,” said Burks. “So much happened on that site—it was a very busy place over a very long period of time—and we’re still grappling with understanding it all. We’ve just got to keep trying.” Lost Coil

DAVID MALAKOFF is a deputy news editor at Science magazine in Washington, D.C. He is a frequent contributor to American Archaeology.