The Great Serpent Mound is a 1,348-foot (411 m)-long, three-foot-high prehistoric effigy mound on a plateau of the Serpent Mound crater along Ohio Brush Creek in Adams County, Ohio. Maintained within a park by the Ohio History Connection, it has been designated a National Historic Landmark by the United States Department of Interior. The Serpent Mound of Ohio was first reported from surveys by Ephraim Squire and Edwin Davis in their historic volume Ancient Monuments of the Mississippi Valley, published in 1848 by the newly founded Smithsonian Museum.
Researchers have attributed construction of the mound to three different prehistoric indigenous cultures. Originally thought to be Adena in origin, a 1996 carbon dating study led scholars to believe the mound was built by members of the Fort Ancient culture around 1070 CE. Most recent dating places the mound at around 300 BCE, once again suggesting Adena construction. Serpent Mound is the largest serpent effigy in the world.