The Great Serpent Mound

The largest effigy mound on Earth, on an ancient impact crater

On a bluff above Ohio Brush Creek in Adams County, Ohio, an earthen snake uncoils for 1,348 feet, the largest serpent effigy known in the world. It is built mostly of yellowish clay and ash with an outer skin of stone and soil, 22 to 24 feet wide and from nine inches to more than three feet high. Its body winds back and forth for more than 800 feet to a triple-coiled tail, and at the other end its open jaws curve around a hollow oval about 120 feet long. E. G. Squier and Edwin Davis, who published the first survey in 1848 for the Smithsonian, saw a snake swallowing an egg; others see the moon, an eye or a frog. In 1909 a local minister, Landon West, declared that it marked the original Garden of Eden.

Its setting is as odd as its shape. The mound sits on the Serpent Mound crater, a meteorite impact structure about 14 km across, struck 252 to 330 million years ago and long since worn down by erosion. In 1987 Clark and Marjorie Hardman reported that the head and oval line up with the summer solstice sunset and the coiled tail with the winter solstice sunrise, though the sight lines are short enough to leave room for doubt.

Who built it has been argued for a century. Frederic Ward Putnam of Harvard, who excavated it in the 1880s, credited the Adena people, whose burial mounds stand nearby, although he found no Adena artefacts inside the serpent. In 1996 two amateur mappers, Robert Fletcher and Terry Cameron, working with archaeologist Bradley Lepper, recovered charcoal that dated to around AD 1070, pointing instead to the Fort Ancient culture; that date falls close to the supernova of 1054 and the brilliant return of Halley's Comet in 1066, and Lepper admitted it was fun to wonder about a fiery serpent across the sky. In 2014 new radiocarbon dates pushed construction back to about 300 BC, with a repair around 1100; Lepper has countered that those samples came from organic sediment in soil cores, which can run thousands of years too old, and that Fort Ancient people, not Adena, carved serpents into their art. He suggests it may depict the Great Serpent, lord of the Beneath World, from a Dhegihan Siouan origin story.

Putnam saved it. Finding mounds across the Midwest being destroyed by ploughing and development, he raised money with a group of Boston women led by Alice Fletcher and bought 60 acres in 1886. Today the site is a National Historic Landmark, managed by the Ohio History Connection, and security cameras now watch the serpent after vandals damaged nearby mounds.