Serpent Mound is the largest "serpent effigy" known to man. It is a 1/4 mile long mound shaped like a snake and located in Adams County, Ohio. Various alignments of the serpent correspond to astronomical features, such as alignments of the sun and moon. Recent research has found solar alignments and six lunar alignments corresponding to six coils of the serpent effigy. This suggests that the builders of Serpent Mound were a society of Native American astronomers. A picture of the mound can be seen here. There are similar serpent effigies located in Scotland and Ontario.

The bottom of the mound is clay and rock, with soil covering the rock 4-5 feet high. The shape is thought by some to like a serpent with it's mouth open, about to devour an egg. Others have speculated that it represented the myth of the horned serpent found in many Native American and American Indian cultures. Archeologists have studied the site since at least the late nineteenth century. Historians have generally believed that the mound was build by the Adena culture (800 BC-AD 100). Two nearby burial mounds are also attributed to this culture. A third burial mound can be found at the at the Serpent Mound State Memorial and a village site near the effigy's tail belong to the later Fort Ancient culture (AD 1000-1550).