Serpent Mound: A Mysterious 400-Meter Snake Lurks In Ohio’s River Valley

Ohio’s Serpent Mound might just be one of the most fascinating prehistoric sites in North America. Located in Adams County, it’s the largest known surviving example of a prehistoric effigy mound in the world. Its origins remain unclear. Who built this amazing monument and why? Fortunately, modern science is helping to shed light on the mystery.

It almost looks as if a giant serpent is lying beneath a shallow sprinkling of earth and grass, consisting of a gently raised mound that snakes around for 411 meters (over 1,300 feet), according to UNESCO. At one end of the swirling mound is a large oval shape, which has been interpreted as a snake’s head, eye, or perhaps an egg clenched in the reptile’s mouth.

The monument is an example of an effigy mound, earthworks formed in the shape of animals that were built by Native American cultures in parts of present-day Wisconsin, Minnesota, Illinois, Iowa, and Ohio. Similar monuments have been found as far south as Peru, hinting at a strong cultural bond that runs through the Americas. 

The origins of the Serpent Mound were hotly debated by archaeologists and anthropologists throughout the 20th century. Some effigy mounds feature human burials and physical artifacts that help to illuminate the people who constructed them. No such discoveries have been made at Serpent Mound, though.

Who built the Great Serpent Mound? It still isn’t certain.
Image credit: Oh London Tom/

In more recent years, archaeological advances have been getting to the bottom of the mystery – although many questions remain. One load of radiocarbon dating results has suggested that the Serpent Mound emerged around 1120 CE, which would indicate it was built by the Fort Ancient Culture, a Native American culture that flourished in and around the Ohio River valley between 1000 to 1500 CE. 

However, another team of archaeologists published new radiocarbon dates in 2014, suggesting that it was built around 300 BCE by the Adena culture, according to the Ohio History Connection.

Whoever built this monument, the mound most likely held a huge cultural significance. It’s been noted that the head of the serpent aligns with the summer solstice sunset and the tail points to the winter solstice sunrise, leading to suggestions that it had some astronomical function.

Sadly, the site fell into ruin by the 19th century as a result of rampant farming and looting. By 1887, however, it started to undergo restoration and has since been designated as a National Historic Landmark by the United States Department of the Interior.

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