The Portsmouth Earthworks formed a vast prehistoric mound and enclosure complex at the meeting of the Scioto and Ohio rivers around present-day Portsmouth, Ohio, with sections extending into Kentucky. Built by Adena and Ohio Hopewell peoples between about 100 BCE and 500 CE, they ranked among the largest Hopewell ceremonial centers in eastern North America. The complex once extended more than twenty miles through the Ohio River valley in four main sections, with enclosures, roads, and mounds linking spaces across the landscape. Although much has been destroyed by modern development, surveys and surviving features preserve evidence of a major ceremonial landscape and a significant monument-building tradition in the Ohio Valley.