Serpent Mound

Why this is extraordinary

On a bluff above Ohio Brush Creek, people raised an earthen ridge in the plan of a serpent, several hundred metres from the coiled tail to the oval at the head. It is the largest serpent effigy in North America. Burial mounds sit nearby, and a short walk south brings you to the traces of a later village. The snake has been offered to two cultures that never lived at the same time.

For a long time the effigy was Adena, the Early Woodland people of the last centuries before the common era, because Adena mounds and burials sit on the same ground. Charcoal from undisturbed fill in the body then dated near AD 1070, which lands in the Fort Ancient centuries. A 2014 campaign cored the base, dated the organic sediment to about 2,300 years ago, and read that as an Adena construction later repaired by Fort Ancient hands. The catch is that charcoal and humus in an old soil can be centuries older than the day a basket was emptied on top of them. Bulk dates from a mound often date the ground, not the building. Follow that reply and the serpent could have been raised any time after about 300 BC, with the charcoal in the fill as the closer clock.

The head has been lined up with the summer-solstice sunset. The summer solstice is the longest day, and on that evening the sun sets farther north than on any other day of the year. A sightline is a direction you can check by looking. You stand so the oval and the neck lie between you and the western skyline, and you watch whether the sun goes down along them. The Ohio History Connection describes the head and the oval as aligned to that setting sun. Across the centuries that separate Adena from Fort Ancient, the sun’s setting place at midsummer barely moves, less than the uncertainty of a local horizon and less than an earthwork several metres wide, so a solstice sightline, if it is real, does not date the snake.

A 2022 reconstruction aims the head-to-tail line at Scorpius, and then at the bright star in that constellation, on the summer-solstice night, in both the earlier and the later candidate century. A north–south ridge points at the southern summer sky anyway. No azimuth is copied here. A 1994 survey newsletter suggests the bright comet of 1066 as the model if the charcoal near 1070 is construction rather than repair. That is not a horizon measurement, and the same century is already the village.

What the serpent and that sunset meant to the people who raised the ridge is not written on the earth. Later traditions offer possible meanings, and they are not a transcript. A published account of eastern woodlands traditions describes the Great Serpent as a power of the waters and caverns under the earth, and, in some tellings, a presence in the night sky as well. Viewers have called the oval an egg, an eye, or an open mouth. A further reading takes the earthwork as an episode in a creation story of the Great Serpent and First Woman, told among Dhegiha Siouan peoples. The Ohio History Connection, writing with the Shawnee Tribe, says that reading does not show whose ancestors built the mound, and that the story, or a close variant, may once have been shared widely. Shawnee tradition includes a woman creator with many of First Woman’s traits, and a Snake Clan in the traditional religious community. Shawnee people returned to the mound for the summer solstice in 2021 and treat the place as sacred. That is a living use of the day. The sources used here do not describe a solstice ceremony from the year the ridge was raised.

Under the bluff the age is of another kind. The Ohio geological survey describes an impact structure about eight miles across, struck between about 252 and 330 million years ago, and the effigy sits on the eroded southwestern rim. The crater is not the mound, and the mound is not the crater.