This complex, built by the Hopewell culture between 100 BCE and 400 CE, contains the largest earthen enclosures in the world, and was about 3,000 acres (1,200 ha) in total extent.

"[2] This is part of the Hopewell Ceremonial Earthworks, one of 14 sites nominated in January 2008 by the U.S. Department of the Interior for potential submission by the United States to the UNESCO World Heritage List.

[3] It was officially designated a World Heritage Site in September 2023 together with the earthworks at Hopewell Culture National Historical Park and Fort Ancient.

[4] Built by the Hopewell culture between 100 BCE and 400 CE,[5] the earthworks were used by the indigenous Native Americans as places of ceremony, social gathering, trade, worship, and honoring the dead.

Scholars have demonstrated that the Octagon Earthworks comprise a lunar observatory for tracking the Moon's orbit during its 18.6-year cycle.

[6] The complex was one of hundreds of Native American ancient monuments identified and surveyed for the Smithsonian Institution in the mid-nineteenth century by Ephraim G. Squier and Edwin Hamilton Davis, from 1837 to 1847.

Activists have pressed for more public access to the site to witness the moonrise, which observance was planned in the design and construction by the original native builders.

The Newark square's sides formerly ranged from about 940 feet (300 m) to 950 ft (300 m) in length, enclosing a total area of about 20 acres (8 ha).

[6] Much of the square enclosure and its associated mounds was destroyed during nineteenth-century European-American development: construction related to building the Ohio Canal, as well as the streets and houses of the city of Newark.