The Great Serpent Mound of Ohio - An Ancient Snake Effigy

New Dates for Ohio's Enormous Native American Serpent Effigy

Coils of Serpent Mound, Ohio
Coils of Serpent Mound, Ohio. peggydavis66

The Great Serpent Mound, or just Serpent Mound, is a long, sinuous, earthen effigy mound, perched atop a cliff in Adams County, south central Ohio in the American midwest. While the age of the construction is somewhat under debate, the latest work (2014) suggests that it was built during the Early Woodland Adena period, and repaired and reused during the Prehistoric Fort Ancient period some 1500 years later, an astonishing length of time if correct.

The earthen effigy of an enormous snake on a bluff above the perennial Brush Creek. The snake effigy measures about 400 meters (1,300 feet) long, with three main coils, a tight spiral at the southeast tail end, and an ornate triangle and double oval embankment at the northwest end, measuring 37x18 m (121x59 ft). The mound today measures an average of 1.2-1.5 m (4-5 ft) in height throughout its body, and about 30 centimeters (1 ft) near its tail; it almost certainly was higher when first constructed. The width of the body varies between about 6-7.6 m (20-25 ft).

Serpent Mound is in a state-owned park, open to visitors year round when the weather permits. To the west of the Serpent mount is a steep cliff above Brush Creek. On the steep cliff exposure that extends out from the top of Serpent Mound is a natural rock formation that resembles a colossal head. The Serpent Mound is also near a famous geological formation of the same name, about 8 kilometers (5 miles) in diameter, which is believed to represent an Ordovician erosional feature about half a million years old.

Who Built Serpent Mound?

Most effigy mounds are not artifact-rich: they are simply earthen monuments built of excavated soil. That is true for Serpent Mound as well, and as with all effigy mounds, that makes it difficult to determine when it was built. Before the advent of the radiocarbon method of dating in the 1940s, the artifacts found within a mound were the major way of telling who built the mound and when.

The earliest interpretations of Serpent Mound were that it was constructed during the Early Woodland period by the Adena culture (500 BC-AD 200). That interpretation was based on excavations of a nearby conical mound located about 200 m (650 ft) southeast of Serpent Mound, excavated by pioneering archaeologist Frederick Putnam and analyzed by James B. Griffin, who reported pottery and tools dated to both Adena and Fort Ancient periods (AD 1000-1650).

Dating Controversy

Excavations by Putnam in the 1880s recovered almost nothing from Serpent Mound itself. Fletcher and colleagues (1996) reopened Putnam's trench in the mound and found charcoal below the mound level, which was radiocarbon dated to 920 +/- 70 RCYBP, indicating a Fort Ancient construction, 1500 years later than the original estimates.

A few artifacts were found by Fletcher et al. when they reopened Putnam's trench, mostly stone flakes and bladelets, mostly of local Vanport chert from nearby Flint Ridge. The few pottery sherds were unclassified grit-tempered Woodland cord-marked, textile and smoothed ceramics. Calibrated AMS dates taken on wood charcoal in this trench ranged between 1000-1140 AD. On that basis, Fletcher et al.

assigned Serpent Mound to a Late Woodland-early Late Prehistoric.

Dating Serpent Mound's Construction--and Use

In the 21st century, Herrmann and colleagues (2014) used sediment core analysis on Serpent Mound, a technique that involves drilling small holes into the mound rather than complete excavation, which would have damaged the monument. They obtained ten new carbon samples from different parts of the mound. Those returned a wide range of radiocarbon dates, revealing that a far more complex construction and use history. Most importantly, Herrmann et al. identified a preconstruction paleosol--a level of topsoil buried beneath the mound at the time of its construction. Charcoal within that paleosol indicate the topsoil was buried between 381-44 cal BC, firmly setting the construction during the Early Woodland Adena period.

Putnam and Griffin were right.

In the 2014 discussion, however, the evidence compiled by Fletcher and colleagues should be interpreted as a Fort Ancient reconstruction episode 900 years ago, perhaps to repair a sinkhole or other problem. Whether the mound was in continuous use or not is not clear, although Herrmann and colleagues identified remnants of a possible discontinued fourth coil near the head of the serpent.

Interpretation of the Serpent Motif

At the time of its rediscovery in the mid-19th century, the mound was in old growth forest, and it had been completely missed--or at least went unreported--by Caleb Atwatwer's 1820s investigation of Ohio mounds. The first map was drawn by Squier and Davis in 1846. Its detailed complexity proved remarkably difficult to map, and further attempts were drawn by J. P.

McLean (1885), W. H. Holmes (1886), and C. C. Willoughby (1919), most of whom were later accused of overinterpretation of the existing data. McLean, quoted by Willoughby in 1919, said this in describing Serpent Mound:

A serpent is on the mainland, resting in a coil, hid by a slight depression, and protected by declivities at two points of the compass. While in this position it beholds a frog sitting near the point of land beyond. The serpent unfolds itself glides along the edge of the mainland until it reaches the tongue or spur, drops its head into the declivity, and just as it reaches the highest point beyond, strikes at the frog. But the wily batrachian becomes alarmed, leaps in time, and emits an egg which in turn is injected into the mouth of the serpent. McLean quoted by Willoughby 1919

The stylistic motif of the ornate triangle and oval head, albeit damaged by a tornado and agricultural work since its rediscovery, has been likened to a range of cultural snake motifs, from Early Woodland and Late Prehistoric, and much earlier and much later, including Mississippian rattlesnake gorgets carved from shell, and the iconic underwater panther.


Impact Crater?

Adjacent to Serpent Mound is an anomalous geological feature that resembles an impact crater, although there is debate about its origins in geological circles. The feature is a nearly circular region of about 8 km in diameter of faulted and folded Paleozoic carbonates, sandstones and sheles with a central core with ~300 meters of uplift, which was subsequently eroded.

Carlton et al. (1998) identified evidence of shock metamorphism but only minor amounts of meteorite elements (Cr, Co, Ni, and Ir). Dating of Ordivician carbonates within the feature indicate a range of deposition between 445-472 million years ago (Widom 2004); Widom concluded it was an erosional feature, rather than a meteorite impact.

History of Investigations

Serpent Mound was first mapped and published by the American surveyors Squier and Davis in 1846, who were investigating local reports of a defensive structure. The first excavations were conducted by Frederick W. Putnam of the Peabody Museum, who trenched across the effigy and nearby mounds in 1887-1889. Putnam was also instrumental in is preservation, aided by his student and future anthropologist Alice C. Fletcher. After his excavations, Putnam converted it into a public park, which was deeded to the Ohio Historical Society in 1900.

Excavations by Fletcher and colleagues (1996) were conducted in the summer of 1991; Hermann et al. conducted core sampling at the site in 2011.

For another take on Serpent Mound, see:


    Carlton RW, Koeberl C, Baranoski MT, and Schumacher GA. 1998. 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 162(1–4):177-185. doi: 10.1016/S0012-821X(98)00166-6

    Fletcher RV, Cameron TL, Lepper BT, Wymer DA, and Pickard WH. 1996. Serpent Mound: a Fort Ancient icon? Midcontinental Journal of Archaeology 21(1):105-143.

    Herrmann EW, Monaghan GW, Romain WF, Schilling TM, Burks J, Leone KL, Purtill MP, and Tonetti AC. 2014. A new multistage construction chronology for the Great Serpent Mound, USA. Journal of Archaeological Science 50(0):117-125. doi: 10.1016/j.jas.2014.07.004

    Holmes WH. 1886. A Sketch of the Great Serpent Mound. Science 8(204):624-628.

    Widom E, Gaddis SJ, and Wells NE.

    2004. Re-Os isotope systematics in carbonates from Serpent Mound, Ohio: Implications for Re-Os dating of crustal rocks and the osmium isotopic composition of Ordovician seawater. Geochemistry, Geophysics, Geosystems 5(3):Q03006. doi: 10.1029/2002GC000444

    Willoughby CC. 1919. The Serpent Mound of Adams County, Ohio. American Anthropologist 21(2):153-163. doi: 10.2307/660267