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The Newark Earthworks, in and around the modern city of Newark, Ohio, were constructed between roughly 100 BCE and 400 CE by people of the Hopewell culture — a term archaeologists use not for a single unified society but for a widespread network of related communities across the eastern woodlands of North America, connected by shared ceremonial practices, artistic styles, and an extraordinary long-distance exchange system. Originally covering some seven square kilometres, the Newark complex was the largest concentration of geometric earthen enclosures in the Hopewell world, and the largest such geometric earthwork complex known anywhere on the planet.
The surviving portions — much of the complex was destroyed by 19th- and 20th-century urban development and agriculture — include two of the most remarkable individual monuments. The Great Circle, roughly 365 metres in diameter with walls up to 4 metres high enclosing a moat-like interior ditch, is one of the largest circular earthen enclosures in the world. The Octagon Earthworks, connected by parallel walls to a precise circle, enclose an area large enough to contain several dozen American football fields, their embankments forming a near-perfect octagonal figure joined to a circular one.
What elevates Newark beyond sheer scale is the geometric and astronomical sophistication built into its design. Modern survey has shown that the various enclosures share consistent units of measurement and geometric relationships across distances of kilometres, implying careful planning and a shared system of proportion. Most strikingly, research beginning in the 1980s by Ray Hively and Robert Horn demonstrated that the Octagon Earthworks are aligned to the complex 18.6-year cycle of the moon — the slow oscillation of the points on the horizon where the moon rises and sets, known as the lunar standstill cycle — with the octagon's walls and openings marking the moon's extreme rising and setting positions. Tracking this cycle requires sustained, multi-decade astronomical observation, since a single 18.6-year period exceeds a large part of a human lifetime in the ancient world, indicating a remarkable investment in celestial observation and record-keeping.
The Hopewell communities who built Newark were not a centralised state or empire; they lived in relatively dispersed settlements and did not farm intensively in the manner of later Mississippian societies. That such societies could mobilise the collective labour and sustain the astronomical knowledge needed to build and align these enormous, geometrically exact earthworks has made Newark central to understanding the social and intellectual capabilities of non-state, non-urban societies. The Newark Earthworks, together with several other Ohio Hopewell sites, were inscribed as part of the Hopewell Ceremonial Earthworks UNESCO World Heritage Site in 2023.