Serpent Mound

Historically, researchers first attributed the mound to the Adena culture (1000 BC – 100 AD). William Webb, noted Adena exponent, found evidence through carbon dating for Kentucky Adena as early as 1200 BC. As there are Adena graves near the Serpent Mound, scholars thought the same people constructed the mound. The skeletal remains of the Adena type uncovered in the 1880s at Serpent Mound indicate that these people were unique among the ancient Ohio Valley peoples.

An eight-member team led by archaeologist William F Romain has been published in the Journal of Archaeological Science.[12][13] The team found much older charcoal samples in less-damaged sections of the mound. The investigators conjecture that the mound was originally built between 381 BC and 44 BC, with a mean date of 321 BC. They explain the more recent charcoal found in the 1990s as likely the result of a "repair" effort by indigenous people around 1070 AD, when the mound would already have been suffering from natural degradation.

Squier and Davis's map from Ancient Monuments of the Mississippi Valley, published by the Smithsonian Institution Press in 1848

In 1996, the team of Robert V. Fletcher and Terry L. Cameron (under the supervision of the Ohio Historical Society's Bradley T. Lepper) reopened a trench created by Frederic Ward Putnam of Harvard over 100 years before. They found a few pieces of charcoal in what was believed to be an undisturbed portion of the Serpent Mound. However, bioturbation, including burrowing animals, frost cracks, etc., can reverse the structural timeline of an earthen mound such as Serpent Mound. It can shift carbon left by a later culture on the surface to areas deep within the structure, making the earthwork appear younger.

When the team conducted carbon dating studies on the charcoal pieces, two yielded a date of ca. 1070 AD, with the third piece dating to the Late Archaic period some two thousand years earlier, specifically 2920+/-65 years BP (before the present). The third date, ca. 2900 BP, was recovered from a core sample below cultural modification level. The first two dates place the Serpent Mound within the realm of the Fort Ancient culture. The third dates the mound back to very early Adena culture or before.[14]

The Fort Ancient people could have been the builders of the Serpent Mound. Alternatively, they may have refurbished the earthwork for their own use in the same way that people today fix up old houses to make them suitable for occupation again. The rattlesnake is significant as a symbol in the Mississippian culture, which would help explain the image of the mound. However, there is no sign or indication of a rattle.[14]

If this mound was built by the Fort Ancient people, it was uncharacteristic for that group. For example, the mound does not contain artifacts, although, like the Adena people, the Fort Ancient culture typically buried many artifacts in its mounds. In another difference, the Fort Ancient people did not usually bury their dead in the manner of the burials found in proximity to the effigy.[14]

One of the only other effigy mounds in Ohio, the Alligator Effigy Mound in Granville, was carbon dated to the Fort Ancient period.

The spiral tail at the end of the Serpent Mound

In 1987, Clark and Marjorie Hardman published their finding that the oval-to-head area of the serpent is aligned to the summer solstice sunset.[15][16] William F. Romain has suggested an array of lunar alignments based on the curves in the effigy's body. Fletcher and Cameron argued convincingly for the Serpent Mound's coils being aligned to the two solstice and two equinox events each year. If the Serpent Mound was designed to sight both solar and lunar arrays, it would be significant as the consolidation of astronomical knowledge into a single symbol. The head of the serpent is aligned to the summer solstice sunset and the coils also may point to the winter solstice sunrise and the equinox sunrise.[17]

A depiction of the serpent mound that appeared in The Century periodical in April 1890, drawn by William Jacob Baer.

If 1070 AD is accurate as the construction year, building the mound could theoretically have been influenced by two astronomical events: the light from the supernova that created the Crab Nebula in 1054, and the appearance of Halley's Comet in 1066.[18] The supernova light would have been visible for two weeks after it first reached earth, even during the day. The Halley's Comet's tail has always appeared as a long, straight line and does not resemble the curves of the Serpent Mound. Halley's comet appears every 76 years. Numerous other supernovas may have occurred over the centuries that span the possible construction dates of the effigy.

Hopewell pipe, points, and earspool on display at Serpent Mound

Gorgets and points from the Adena culture, found at Serpent Mound

After raising sufficient funds, in 1886 Putnam returned to the same site. He worked for four years excavating the contents and burial sequences of both the Serpent Mound and two nearby conical mounds. After his work was completed and his findings documented, Putnam worked on restoring the mounds to their original state.

One of the conical mounds that was excavated by Putnam (1890)[28] yielded a principal burial which has grave goods that associate it with the Adena period (800 BC-100 BC). He also found and excavated nine intrusive burials in the mound. Additionally, Putnam discovered an ash bed north of the conical mound that contained many prehistoric artifacts. After the excavation, the conical mound was reconstructed and is today standing south of the parking lot at Serpent Mound State Memorial.

In 2011, excavations were undertaken prior to installation of utility lines at Serpent Mound State Memorial. The excavations focused on three sides of the conical mound that Putnam (1890) had excavated. In addition to concentrations of artifacts, an ashy soil horizon was excavated north of the conical mound. The ashy soil horizon had prehistoric artifacts associated with them. It is believed that the ashy deposit is a remnant of the ash bed that Putnam (1890) excavated. Wood charcoal from within the remnant ash bed was carbon dated to 1041-1211 AD, the Fort Ancient period. Because the burials in the conical mound dated to the Early Woodland period, the Fort Ancient period dating of the remnant ash bed is suggestive of ritual reuse of the circum mound area.[29]

A digital GIS map of Ohio's Great Serpent Mound, created by Timothy A. Price and Nichole I. Stump in March 2002

In 1901, the Ohio Historical Society hired engineer Clinton Cowan to survey newly acquired lands. Cowan created a 56 by 72-inch (1,800 mm) map that depicted the outline of the Serpent Mound in relation to nearby landmarks, such as rivers. Cowan also made specific geographical surveys of the area, and he discovered the unique astrobleme on which the mound is based. He found that the mound is at the convergence of three distinctly different soil types. Cowan's information, in conjunction with Putnam's archaeological discoveries, has been the basis for all modern investigations of the Serpent Mound.

In 1967, the Ohio Historical Society opened the Serpent Mound Museum, built near the mound. A pathway was constructed around the base of the mound to help visitors. The museum features exhibits that include interpretations of the effigy's form, description of the processes of constructing the mound, the geographical history of the area, and an exhibit on the Adena culture, historically credited as the creators of the mound.

Serpent Mound State Memorial is currently being operated on behalf of the Ohio Historical Society by the Arc of Appalachia Preserve System. It is a non-profit organization specializing in the preservation and protection of native biodiversity and prehistoric aboriginal sites in southern Ohio.