Serpent Mound in Ohio is the largest serpent effigy in the world, built c. 1000 AD by the Fort Ancient culture atop an ancient meteor impact crater. Its head aligns with the summer solstice sunset and its coils with other solar and lunar events. While impressive, earthen mound building was a widespread tradition among Eastern Woodlands peoples for over 2,000 years. The meteor crater beneath was created approximately 300 million years ago — long before human habitation.