The Great Serpent Mound is a 1,330-foot-long, three-foot-high prehistoric effigy mound located on a plateau of the Serpent Mound crater along Ohio Brush Creek in Adams County, Ohio. Maintained within a park by the Ohio Historical Society, 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. Based on the use of more advanced technology, including carbon dating and evidence from 1996 studies, many scholars now believe that members of the Fort Ancient culture built it about 1070 CE (plus or minus 70 years). There are still anomalies to be studied. Serpent Mound is the largest serpent effigy in the world.