The Portsmouth Earthworks are a large prehistoric mound complex constructed by the Native American Adena and Ohio Hopewell cultures of eastern North America (100 BCE to 500 CE).

It was surveyed and mapped by E. G. Squier in 1847 for inclusion in the seminal archaeological and anthrolopological work Ancient Monuments of the Mississippi Valley.

[2] In 2019 two independent scholars proposed that the Group B mounds represent part of an eight-mile-long female effigy mound, which the authors propose depicts "The Woman Who Fell from the Sky," a Native American myth about human origins found among the indigenous peoples of North America.

It is also the location of Lower Shawneetown, a protohistoric/historic Fort Ancient and Shawnee settlement and colonial trading post which are all part of the Lower Shawneetown Archeological District,[7] along with the Thompson and Hansen sites Group C was a large series of concentric circles surrounding a high central conical mound.

This section of the earthworks is located in Greenup County, Kentucky several miles to the east of South Shore, but connected to Group B by a causeway that ran down to the Ohio River.