serpent mound is a quarter mile long prehistoric effigy mound. when it was built and by whom are debated by scholars and others. the most common belief is that it was built around 1000 ce (ad). it was possibly constructed by the fort ancient culture. other suggestions have been the hopewell culture and the adena culture. the head of the serpent is aligned with the summer solstice sunset. the mound is also located within an unusual geological area known as a crypto-explosion structure. in other words, and as i understand it, either something volcanic or meteoric impacted the area. anyway, the place is steeped in mystery. its purpose and meaning are still debated.