A publication of the Archaeological Institute of America
New radiocarbon dates suggest that Serpent Mound, a one-quarter-mile-long earthen effigy of a snake in south-central Ohio, was built as many as 2,000 years later than previously thought. The effigy had been attributed to the Adena culture (1000-100 B.C.) based on the presence of Adena burials nearby. The Adena people, who lived in an area stretching from the Midwest to the Atlantic coast, collected and began domesticating plants, improved methods of food storage, and buried their dead in mounds. Two samples of wood charcoal were obtained from undisturbed parts of Serpent Mound. Both yielded a date of ca. A.D.1070, suggesting that the effigy was actually built by people of the Fort Ancient culture (A.D. 900-1600), a Mississippian group that lived in the central Ohio Valley. Mississippian people inhabited the Tennessee, Cumberland, and Mississippi river valleys, built huge earthworks, cultivated maize, and were governed by powerful chiefs, ruling families, or both. The Mississippian's centralized authority would have made possible organizing a large building project such as the construction of Serpent Mound. Additional evidence for the later date includes the remains of a Fort Ancient village 100 yards south of the mound and rattlesnake motifs on Mississippian gorgets (ornaments worn on the chest) made from marine shell.
The new dates are the result of work by University of Pittsburgh archaeology student Robert V. Fletcher, who noticed that maps of the mound were out of date. He and a friend, Terry L. Cameron, began to remap the site on weekends. Serpent Mound had not been scientifically investigated since the late 1880s, when Frederick W. Putnam of Harvard's Peabody Museum mapped the mound and excavated sections of the serpent's sinuous body and oval "head" (upper right in photo), which has also been described as an egg or an enlarged eye. Putnam attributed the creation of Serpent Mound to the Adena culture even though he found no Adena artifacts within the serpent itself. Fletcher and Cameron wanted more solid evidence with which to date the effigy, so they contacted archaeologists Bradley Lepper, a curator at the Ohio Historical Society, and Dee Anne Wymer, of Bloomsburg University, who took core samples and conducted the limited excavations that yielded the samples for dating.
Other studies indicate that features of Serpent Mound are aligned with both the summer solstice sunset and, less clearly, the winter solstice sunrise. A pile of burned stones once located inside the oval head area was several feet northwest of its center, possibly to make a more precise alignment with the point of the "V" in the serpent's "neck" and the summer solstice sunset. The A.D. 1070 date coincides roughly with two extraordinary astronomical events. Light from the supernova that produced the Crab Nebula first reached Earth in 1054 and remained visible, even during the day, for two weeks. The brightest appearance ever of Halley's Comet was recorded by Chinese astronomers in 1066. Could Serpent Mound have been a Native American response to such celestial events? "It is impossible to test whether or not the effigy mound represents a fiery serpent slithering across the sky," says Lepper, "but it is fun to speculate."