From Ohio History Central
The High Bank Earthworks consist of a large circular embankment connected to an octagonal enclosure located along the Scioto River southeast of Chillicothe, Ohio. The circle is 1,050 feet in diameter and encloses 20 acres. The octagon is 950 feet across and encloses 18 acres. The walls of the octagon originally were 11 to 12 feet in height. The earthworks have been plowed nearly flat, but some traces remain and the outlines can be traced from above. The surviving remnants are one component of the Hopewell Culture National Historical Park.
High Bank Earthworks and the Octagon Earthworks in Newark, Ohio appear to be related in important ways. They are the only two circle-and-octagon combinations built by the Hopewell culture (100 B.C. to 500 A.D.) of prehistoric Native American people. The circular earthwork at High Bank is the same size as the circular enclosure linked to the octagon at Newark. Ray Hively and Robert Horn, of Earlham College, believe that both of these earthworks served as astronomical observatories. Both earthworks incorporate alignments to the rising and setting of the moon through its 18.6-year cycle. The High Bank Earthworks also include alignments to the summer and winter solstice sunrises and sunsets.
The High Bank Earthworks are listed on the National Register of Historic Places. The site is occasionally confused with a Late Woodland location called Highbanks Park Earthworks in Delaware County, Ohio.