The Portsmouth Earthworks were constructed from 100 BCE to 500 CE. It is a large ceremonial center located at the confluence of the Scioto and Ohio rivers. Part of this earthwork complex extends across the Ohio River into Kentucky. The earthworks included a northern section consisting of a number of circular enclosures, two large, horseshoe-shaped enclosures, and three sets of parallel-walled roads leading away from this location. One set of walls went to the southwest and may have linked to a large square enclosure located on the Kentucky side of the Ohio River. Another set of walls led to the southeast, where it crossed the Ohio River and continued to the Biggs site, a complicated circular enclosure surrounding a conical mound. The third set of walls went to the northwest for an undetermined distance, in the direction of the Tremper site.