The Octagon Earthworks were once the center of an ancient civilization and a focal point for the social and religious activities of the Hopewell people about 2000 years ago. Part of the Newark Earthworks, the largest set of geometric earthen enclosures ever built, they include a nearly perfect circle 1,050 feet in diameter and an octagon more than 1,500 feet across. They may have been built as an astronomical observatory, with many walls and gateways aligned to points on the horizon marking key moonrises and moonsets in a complicated 18.6 year lunar cycle. The earthworks were preserved and partially restored by the Ohio State Militia, now the National Guard, beginning in 1892, and the site served as their permanent encampment, Camp McKinley, until 1908. In 1910, the Newark Board of Trade began leasing the site to Moundbuilders Country Club for use as a golf course. The Ohio Historical Society acquired the site in 1933, and Moundbuilders Country Club operates the site under a lease from the Ohio Historical Society.