The Newark Earthworks in Newark and Heath, Ohio, are the largest surviving Hopewell earthwork complex in North America, built between 100 BCE and 400 CE for ceremony, gathering, trade, worship, and honoring the dead. Once spanning about 3,000 acres, the complex survives in three main sections: the Great Circle, the Octagon, and the Wright Earthworks. The Octagon is especially significant as a lunar observatory aligned to the Moon’s 18.6-year cycle, showing remarkable precision. Though later altered by militia use, golf-course development, and other damage, the earthworks have remained central to archaeology and preservation, gaining National Historic Landmark status and UNESCO World Heritage recognition.