Claim: Portsmouth Earthworks ( a large prehistoric mound complex) City of Portsmouth maintains a public park and was listed on the National Register of Historic Places in 1974.
Evidence: The Portsmouth Earthworks are a large prehistoric mound complex constructed by the Ohio Hopewell culture mound builder indigenous peoples of eastern North America (100 BCE to 500 CE). The City of Portsmouth maintains a public park which includes one of the remaining horseshoe-shaped enclosures, known as Mound Park, it is the only publicly accessible part of the complex. Under the name Horseshoe Mound it was listed on the National Register of Historic Places in 1974.