The Newark Earthworks in central Ohio comprise the largest complex of monumental geometric earthen enclosures ever built by the Hopewell culture (A.D. 1–400). The site originally encompassed more than four square miles (ten square kilometers) and included two gigantic circles, an even bigger ellipse, a square, and an octagon—all connected by a network of parallel walls. In addition, there were numerous smaller circular enclosures, mounds of various shapes and sizes, a second large square just …