The Great Serpent Mound is a 1,330-foot long, three-foot-high prehistoric effigy mound located on a plateau along the edge of the Serpent Mound meteor crater in Adams County, Ohio. The Serpent Mound is the largest effigy mound in the world.

Researchers have attributed construction of the mound to three different prehistoric indigenous cultures. It was once thought to be Adena in origin (1000BC-1AD), as there are Adena graves near the Serpent Mound.

Now based on the use of more advanced technology, including carbon dating, many scholars now believe that members of the Fort Ancient culture built it about 1070 AD. There are still anomalies to be studied, which may throw off the timeline further.

Conforming to the curve of the land on which it rests, with its head approaching a cliff above a stream, the serpent winds back and forth for more than eight hundred feet with seven coils and ends in a triple-coiled tail. The serpent head has an open mouth extending around the east end of a long hollow oval feature. Scholars have surmised that the oval feature symbolizes everything from an egg, to the sun, to the body of a frog, or merely the remnants of a platform.

The Cherokee relate the mound to the legend of the Uktena, a large serpent with supernatural appearance and power. If 1070 CE is accurate as the construction year, building the mound could have been influenced by an astronomical event: the appearance of Halley's Comet in 1066.