Travel with Billy Carson — Serpent Mound, also called the Great Serpent Mound, is an earthen effigy of a snake on a bluff above Ohio Brush Creek in Adams County, Ohio, near the village of Peebles. It runs about 1,348 feet (411 m) along its curves, making it the largest known serpent effigy in the world. Archaeologists still disagree over who built it: the Adena culture around 300 BCE, or the Fort Ancient culture around 1100 CE.
The site matters because it sits where several open questions overlap. It is one of the most recognisable earthworks built by Native Americans, it is the subject of a live dating dispute between professional archaeologists, it attracts claims about solstice and star alignments, and it stands on top of a confirmed meteorite impact structure. Each thread has a different level of evidence behind it.
What is Serpent Mound and where is it?
Serpent Mound is a low, sinuous embankment of earth shaped like a snake, built on a plateau in south-central Ohio. The body rises from about 9 inches to a little over 3 feet high and is roughly 20 to 25 feet wide. It winds in a series of S-shaped curves along the ridge, ending at one end in a tight spiral coil.
At the other end, near the edge of the bluff, the head opens into what is usually described as a pair of jaws around an oval enclosure. What that oval represents is one of the site's enduring puzzles. It has been read as an eye, as an egg about to be swallowed, as the sun, and as a frog.
The site is owned by the Ohio History Connection, the state's historical society, which has managed it directly since 2021 after a period when the Arc of Appalachia Preserve System ran it. Serpent Mound was designated a National Historic Landmark and listed on the National Register of Historic Places in 1966. Nearby are conical burial mounds attributed to the Adena culture, along with evidence of a later Fort Ancient village and burials, which is one reason the question of authorship has been so tangled.
How was Serpent Mound discovered and preserved?
The mound entered the scholarly record in 1848, when Ephraim G. Squier and Edwin H. Davis published a survey and plan of it in Ancient Monuments of the Mississippi Valley, the first volume of the Smithsonian Institution's Contributions to Knowledge series. Their drawing made the effigy widely known.
By the 1880s the land was being farmed and the mound was at risk. Frederic Ward Putnam of Harvard's Peabody Museum of Archaeology and Ethnology raised money to buy the site in 1886, with crucial help from a group of Boston women organised by the ethnologist Alice C. Fletcher. Putnam excavated parts of the serpent and the nearby mounds, restored the earthwork, and opened it as one of the first archaeological parks in the country. In 1900 the property was transferred to the Ohio State Archaeological and Historical Society, the forerunner of today's Ohio History Connection.
Putnam's restoration matters to every later debate, because researchers must separate original soils from ancient repairs and from his reshaping.
Who built Serpent Mound?
Serpent Mound was built by ancestral Native American people, but which culture built it is unresolved. The two candidates are the Adena culture, which flourished in the Ohio Valley from roughly 800 BCE to 100 CE, and the Fort Ancient culture, which occupied the same region from about 1000 to 1650 CE.
For most of the twentieth century the Adena attribution was standard, largely because Putnam associated the effigy with the Adena burial mounds beside it. That changed in 1991, when Robert V. Fletcher, Terry L. Cameron and colleagues reopened one of Putnam's old trenches and recovered charcoal from inside the body of the serpent. Two radiocarbon dates came back at roughly 1070 to 1120 CE, squarely in the Fort Ancient period. Their results were published in 1996 in the Midcontinental Journal of Archaeology. A third, much older date was treated as material from beneath or mixed into the mound rather than evidence of construction. Over the next two decades many archaeologists came to accept a Fort Ancient origin.
In 2014 a team led by Edward W. Herrmann, with G. William Monaghan, William F. Romain and others, published a new study in the Journal of Archaeological Science. Working from soil cores taken through the mound, they obtained dates that pointed to construction around 300 BCE by Adena people, with repairs or rebuilding by Fort Ancient people around 1100 CE.
In 2018 Bradley T. Lepper, an archaeologist at the Ohio History Connection, and colleagues replied in the Cambridge Archaeological Journal with "Arguments for the Age of Serpent Mound." They argued that the 2014 samples were organic sediment drawn from cores, not charcoal from an exposed and clearly understood construction layer, and that older material can easily be dug up and redeposited when a mound is built. They also pointed to the serpent's imagery, which they connected to serpent and female figures in Mississippian-period art from around 950 to 1025 CE. Their conclusion was that the best available evidence still favours the Fort Ancient culture.
Lepper himself has written that "we still don't know for sure," and that new methods such as optically stimulated luminescence dating of the soils could settle the question. The fair summary is that both an Adena date and a Fort Ancient date have serious professional support, and the age of the serpent remains an open research question.
What about the "Mound Builder" myth?
The idea that a vanished non-Native race built the earthworks of the Ohio and Mississippi valleys was popular in the nineteenth century and has been thoroughly debunked. Cyrus Thomas's 1894 report for the Smithsonian's Bureau of Ethnology surveyed thousands of mounds and concluded that they were the work of the ancestors of Native American peoples.
The real story is more interesting than the myth. Native communities across eastern North America built monumental earthworks over thousands of years, from the great rings of Poverty Point in Louisiana, discussed in the first Americans were engineers, not farmers, to the effigies of the Upper Midwest. Rock art across the continent, covered in the mysterious petroglyphs of North America, shows that serpent imagery had deep roots in Indigenous visual traditions.
Is Serpent Mound aligned to the solstice?
Serpent Mound has been proposed to align with the solstices, but the alignment has not been proven. In 1987 Clark and Marjorie Hardman published a study in Ohio Archaeologist arguing that a line through the oval and the head points toward the summer-solstice sunset, and that the coiled tail points toward the winter-solstice sunrise. Other writers have suggested that the curves of the body mark the equinoxes or phases of the moon.
Proponents of a sky-based reading have also compared the shape of the serpent to the constellation Draco, whose star Thuban was the pole star thousands of years ago, and others to the Milky Way.
Critics point out a basic difficulty. The sightlines involved are short, the head-to-oval line covers only a few dozen feet, and a body with several winding curves offers many possible directions. With enough candidate lines, some will fall close to a solstice or equinox point by chance. A proper test needs the original layout, which Putnam's restoration complicates, and a match better than chance. No consensus has emerged.
Comparisons with other monuments help set expectations. At Chichén Itzá, the famous serpent of light and shadow appears on El Castillo's staircase around the equinoxes, though scholars still debate whether that effect was intended. At Stonehenge, the main axis frames the midsummer sunrise and midwinter sunset, an alignment far better established. In Peru, the Nazca lines show how long the argument over astronomical purpose can run for a set of ground figures. There is no evidence of any connection between Serpent Mound and these sites; they are useful only as examples of how alignment claims are tested.
Is there really a crater under Serpent Mound?
Yes. The mound sits on the Serpent Mound structure, a circular zone of intensely disturbed bedrock in Adams, Highland and Pike counties. The disturbed core is about 4 miles (roughly 8 km) across, and a 2010 study by geologist Keith Milam proposed that the original rim may have been as much as about 14 km wide. Erosion has removed any visible crater shape, so the structure is known from mapped bedrock, drilling and geophysics.
For much of the twentieth century its origin was debated. The geologist Walter Bucher, who mapped it in the 1920s, grouped it with "cryptovolcanic" structures he thought were caused by gas explosions from below. Later the term "cryptoexplosion" was used to cover either a volcanic or an impact cause.
The question was settled in 1998, when Raymond Carlton, Christian Koeberl, Mark Baranoski and Gregory Schumacher published a study in Earth and Planetary Science Letters. Examining samples from a 903 m core drilled into the central uplift, they found quartz grains with multiple sets of planar deformation features, a form of shock damage produced by hypervelocity impacts, along with altered impact-melt fragments. Chemical analyses of the breccias showed small enrichments in chromium, cobalt, nickel and iridium, consistent with a minor meteoritic component. Together these confirmed an impact origin.
The impact deformed rocks of Early Mississippian age, so it must be younger than those layers, which places it at less than about 320 million years ago. Its exact age is not pinned down.
Did the crater influence the builders?
No one knows. It is a striking coincidence that the largest serpent effigy in the world was built on one of the few confirmed impact structures in the eastern United States, and writers have suggested that the builders noticed unusual rock exposures, springs or landforms and treated the place as special. That is speculation. There is no archaeological evidence that the builders understood the geology or chose the site because of it.
The same caution applies to claims that the mound sits on an energy node or ley line. Those ideas belong to a much wider debate, set out in ley lines explained, and they are interpretations rather than measured properties of the site.
Billy Carson's reading
Billy Carson has not published a dedicated video or episode on Serpent Mound, so this article does not attribute a position on the site to him. His wider work on ancient sites returns again and again to the themes that make Serpent Mound compelling to his audience: how ancient builders observed the sky, why serpent symbolism appears in so many cultures, and how much older and more sophisticated human civilisation may be than textbooks allow.
Readers who follow those themes will find them developed in his material on the Anunnaki topic hub, where Carson sets out his broader case about humanity's ancient past, and in the 4BK TV series on megalithic sites. Where alignment and earth-energy ideas appear in this article, they belong to the named researchers, such as the Hardmans, or to proponents, not to Carson.
Watch, read and go deeper
For a visual tour of the world's great ancient monuments and the debates around them, watch Megalithic Mysteries on 4BK TV. The Anunnaki topic hub gathers Billy Carson's work on ancient civilisations in one place. To compare how alignment claims hold up elsewhere, return to the Stonehenge and Chichén Itzá explainers linked above, and for the earth-energy question, the guide to ley lines.
Frequently asked questions
How long is Serpent Mound?
Serpent Mound is about 1,348 feet (411 m) long measured along its curves. Its height ranges from roughly 9 inches to just over 3 feet. It is the largest known serpent effigy in the world.
How old is Serpent Mound?
Its age is disputed. Charcoal dated in the 1990s points to construction around 1070 to 1120 CE by the Fort Ancient culture, while a 2014 soil-core study argued for about 300 BCE by Adena people with later Fort Ancient repairs. The Ohio History Connection's archaeologist says the question is not settled.
Is Serpent Mound a burial mound?
Archaeological evidence does not point to burials in the serpent itself, so it is not regarded as a burial mound. Separate conical burial mounds attributed to the Adena culture stand nearby, and one of them was damaged in 2015 when a driver took a vehicle over it.
What caused the crater under Serpent Mound?
A meteorite impact. A 1998 study found shocked quartz with planar deformation features and traces of meteoritic elements, including iridium, in a deep core from the structure's central uplift. The impact happened less than about 320 million years ago, long before any people lived in North America.
Can you visit Serpent Mound?
Yes. The site near Peebles, Ohio, is operated by the Ohio History Connection, with a path around the effigy, an observation tower and a small museum.
Sources and further reading
- Ephraim G. Squier and Edwin H. Davis, Ancient Monuments of the Mississippi Valley (Smithsonian Institution, 1848)
- Robert V. Fletcher, Terry L. Cameron, Bradley T. Lepper, Dee Anne Wymer and William Pickard, "Serpent Mound: A Fort Ancient Icon?", Midcontinental Journal of Archaeology 21, no. 1 (1996)
- Edward W. Herrmann, G. William Monaghan, William F. Romain and colleagues, "A New Multistage Construction Chronology for the Great Serpent Mound, USA," Journal of Archaeological Science 50 (2014)
- Bradley T. Lepper, James R. Duncan, Carol Diaz-Granados and Tod A. Frolking, "Arguments for the Age of Serpent Mound," Cambridge Archaeological Journal 28, no. 3 (2018)
- Clark Hardman and Marjorie H. Hardman, "The Great Serpent and the Sun," Ohio Archaeologist 37, no. 3 (1987)
- Raymond W. Carlton, Christian Koeberl, Mark T. Baranoski and Gregory A. Schumacher, "Discovery of microscopic evidence for shock metamorphism at the Serpent Mound structure, south-central Ohio: confirmation of an origin by impact," Earth and Planetary Science Letters (1998)
- Cyrus Thomas, Report on the Mound Explorations of the Bureau of Ethnology (Smithsonian Institution, 1894)
