The Octagon Earthwork and its associated Observatory Circle are enormous and precisely engineered earthen monuments built about 2,000 years ago by Indigenous American inhabitants of the Scioto River valley of central Ohio in the midwestern United States. In 1982, the Octagon earthwork was first recognized by the scientific community as a lunar observatory, tracking the movements of the moon as it rises and sets on the horizon. The rise of the full moon over the Octagon at lunar standstill makes this earthwork one of the loveliest of ancient observatories on our planet, and well worth a chapter in Staring into Space.

A Little Background

Serpent effigy of cut mica, Hopewell culture, Turner Group, Mound 4, Little Miami Valley, Ohio, 200 BC to 500 AD. Peabody Museum, Harvard University. Credit: Daderot. CC0 1.0 Universal Public Domain Dedication.
Serpent effigy of cut mica, Hopewell culture, Turner Group, Mound 4, Little Miami Valley, Ohio, 200 BC to 500 AD. Peabody Museum, Harvard University. Credit: Daderot. CC0 1.0 Universal Public Domain Dedication

The Octagon was built by a society of people archaeologists call Hopewell, and the people and proto-language of the ancient engineers are generally referred to as Ancestral Algonquian. That term refers to a diverse set of specific and independent Middle Woodland groups living in the central part of the U.S. roughly between 100 BCE and 500 CE (dates vary geographically).

The groups shared cultural traits: a variety of burial customs; artistic imagery and styles; a primarily horticultural/hunter-gatherer economy including gardening; a broadly egalitarian political structure, and large, precisely laid out geometric earthworks (circles, squares, octagons, crescents, rectangles). Archaeological sites associated with the Scioto river earthworks have produced exotic artifacts (smoking pipes, figurines, axes, breastplates, panpipes) made of materials from distant locations: mica, steatite, and black bear teeth from the Appalachians; galena and pipestone from the Upper Mississippi valley; copper and silver from the Great Lakes; obsidian from Yellowstone; marine shell and shark's teeth from the Gulf and Atlantic coasts. How and why access to far away sources happened fascinates Hopewell scholars, and may well be associated with Newark's astronomical uses.

The "Hopewell Interaction Sphere"

Map illustrating some of the archaeologically-defined cultures sharing traits of the Hopewell Interaction Sphere. Image credit: Herb Roe, 2010. Creative Commons 3.0.
Map illustrating some of the archaeologically-defined cultures sharing traits of the Hopewell Interaction Sphere. Image credit: Herb Roe, 2010. Creative Commons 3.0.

Defined archaeological groups (the tinted globs in the map above) that share some of these traits were spread throughout the central part of North America, in a big fuzzy chunk sometimes spoken of as the Hopewell Interaction Sphere or HIS for short. In the 1960s, archaeologists conceived the HIS as a material expression of a shared religious cult; but more recently scholars such as U.S. archaeologist Christopher Carr (2021) have suggested discarding this term. In this interpretation, the connections between the central Ohio earthworks, distant sources for the material culture, and possible intermediary groups for obtaining those materials don't reflect a specific shared religion, but are best considered part of an inter-regional palimpsest of ideas and cultural concepts that were being communicated. Possibly by canoe.

According to Marti Chaatsmith (2013), currently Associate Director of the Newark Earthworks Center at The Ohio State University at Newark, at the time of the European colonization, the caretakers of the massive earthen monuments included members of the Shawnee, Miami, Wyandotte, Seneca-Cayuga, Delaware, and Ottawa tribes. They lived among the earthworks and other mounds, protecting and honoring them. They may well have been descendants of the makers. By the time Europeans arrived in the area, however, indigenous groups were already experiencing what researchers have called the "shatter zone" when the local populations were in a state of chaos as they sought to deal with colonial expansion, disease, and displacement, and as a result, much important history has been lost (Garner 2023).

Details of the Octagon

Newark Works, Licking county, Ohio. Squier & Davis 1837-1847. Public domain.
Newark Works, Licking county, Ohio. Squier & Davis 1837-1847. Public domain

The Octagon and its associated Observatory Circle are the best preserved elements of the Newark earthworks, which covered an area of about four square miles (1,000 acres). Newark is part of the larger group of eight magnificent and massive Hopewell earthworks in the Ohio heartland. In 2023, the eight Ohio Earthworks were added to the World Heritage List at UNESCO.

The Octagon is made up of a set of eight free-standing earthen walls, each averaging 189.4 m (621 feet) in length. When Ohioan politician and historian Caleb Atwater (1778-1867) mapped the mounds in 1820, the walls were about 10 ft (3 m) tall; today they average about 1.5-1.8 m (5-6 ft) tall, with wide bases of 12 m (40 ft) or more. The measurements have changed over time for a variety of reasons, including erosion from weather, agricultural and construction activities, and reconstruction and repair (Bernardini 2004).

Map of the Newark Octagon as enshrined in the Hopewell Ceremonial Earthworks UNESCO World Heritage Site. Credit: UNESCO. Public domain.
Map of the Newark Octagon as enshrined in the Hopewell Ceremonial Earthworks UNESCO World Heritage Site. Credit: UNESCO. Public domain

At each of the vertices where the walls should meet is a gap, called a gateway; 30 m (100 ft) inside each gateway is an oval flat-topped mound. Connected to the Octagon by a short, 25 m (80 ft)-wide walled avenue is the Observatory Circle, a nearly perfect circle measuring 321 m (1054 ft) in diameter. That diameter, known in archaeological circles as the OCD, is a mathematical key to the geometry of every other earthwork in Newark and a mark of the astonishing precision of the monuments. The number is also reiterated in geometric measurements of several of the other Hopewell monuments in Ohio (Hancock and Lepper 2025).

The Newark Octagon walls enclose an enormous open space, about 50 acres (20 hectares) in area; in fact, the Newark enclosure includes plenty of open spaces, although no clearly defined plazas. Fifty acres could hold a small town or thousands of people in tents. U.S. astronomer/physicist Ray Hively and philosopher Robert Horn (2006) suggest that it is the large scale of the Octagon-Great Circle structure (along with its orientation, shape, and asymmetry) that made the notable accuracy of the astronomical alignments possible.

Discovering the Lunar Aspects

Illustration of the full moon rise during the standstill of 2005, created by the University of Cincinnati's Center for the Electronic Reconstruction of Historic and Archaeological Sites (CERHAS).
Illustration of the full moon rise during the standstill of 2005, created by the University of Cincinnati's Center for the Electronic Reconstruction of Historic and Archaeological Sites (CERHAS).

The Octagon-Circle combination at Newark has been mapped several times since 1820, a rich legacy leading to a research project from Earlham College beginning in the 1970s investigating possible astronomical alignments (Hively and Horn 1982). Their findings comparing the maps to the then-current formation of the earthworks showed that restorations conducted in the 1930s by the state of Ohio had altered the Octagon slightly, essentially "correcting" one of the wall lengths to make it more symmetrical.

Hively and Horn concluded that in its original form, before the symmetry was imposed, the Octagon would precisely monitor the monthly and 18.6 year cycles of the moon. Alignments documented by the walls trace 16 important moments in the lunar cycle, including the farthest north the moon rises and sets on the horizon, and the farthest south the moon rises and sets.

The most spectacular and significant alignment points to the lunar standstill or lunistice, illustrated above. Once every 18.6 years, the moon rises at its most extreme northerly position and sets at its most extreme southerly position. This location on the horizon is more north and south than the sun is at that time. At the peak of the cycle, the Octagon records the occurrence with a breathtaking display; when the moon rises in a direct alignment across the Octagon and Circle. The moon's observable monthly maximum and minimum positions remain within a tiny one-degree range through a period of a little under two years. A detailed description of the periodicity of the lunar movements may be found at JQ Jacobs site Eclipses, Cosmic Clockwork of the Ancients.

A Lunar Calendar

Flickr user György Soponyai spent a week creating a simulacrum of a lunar analemma over Budapest using Stellarium and Photoshop -- analemmas are time-lapse illustrations of the movement of celestial objects. He published his results on Flickr under a Creative Commons license 2.0.
Flickr user György Soponyai spent a week creating a simulacrum of a lunar analemma over Budapest using Stellarium and Photoshop -- analemmas are time-lapse illustrations of the movement of celestial objects. He published his results on Flickr under a Creative Commons license 2.0.

The construction of the Octagon is strong circumstantial evidence that the builders were using a lunar calendar. Archaeologists once believed that calendars tracking time were not invented until agriculture got underway, but that has proven false. Everyone who survives on our earth needs to be aware of their environment, and a calendar tracking time does that. Modern western society runs its life primarily by the solar calendar; that is a pale descendant of the intricate ones our ancient ancestors developed following the movements of the moon, the sun, or a combination of the two. The Babylonians maintained a lunar calendar and both ancient Greek and Hebrew calendars are based on that; odds are the lunar calendar predates the Babylonians by some time.

The solar year is 365 days and five hours long, divided into 12 months alternating between 30 and 31 days long (except for February) with an extra "leap day" thrown in to correct for the five hour discrepancy once every four years. The lunar calendar is 354 days and eight hours long, divided into 12 months, alternating between 29 and 30 days in length with an extra month added in once every three years.

The Myaamia Lunar Calendar Project

One helpful way to grasp the lunar calendar in reference to our solar one is investigating the Myaamia (Miami) Lunar Calendar Project for reference. Part of a cultural revitalization effort known as The Myaamia Project, the Myaamia Tribe of Oklahoma working with Miami University began recreating their lunar calendar about 20 years ago, to aid in language revitalization, increase the knowledge of traditional land-use customs, and aid in ethnobotany efforts. The Shanati Project is doing the same thing for the Babylonian calendar.

One critical aspect of the lunar calendar is its connection to the environment. Each month in the Myaamia calendar has a name, reflecting a natural event of importance. For example, the Sandhill Crane Moon (cecaahkwa kiilhswa) falls in April/May when the Sandhill cranes return to the Indiana homeland from their winter nesting grounds. Month names vary with the location of the users, adapting to those specific circumstances. The name is not simply a reminder of seasonality, it is seen as an opportunity to reconnect with the natural world (Voros 2009). Have the sandhill cranes returned yet?

Who Watched the Moon Rise at Lunistice?

A view of the Hopewell Ceremonial Earthworks commemoration event area at the Mound City Group. NPS Photo / Tom Engberg.
A view of the Sept. 19, 2023 Hopewell Ceremonial Earthworks commemoration event area at the Mound City Group. NPS Photo / Tom Engberg.

Clearly, ideas were shared across wide expanses — the provision of socially meaningful imported artifacts for burials had to have been accomplished somehow. Carr and colleagues suggest that the connections might have been supported by long-distance intermarriage, pilgrimage to power places in nature and ceremonial centers such as Newark, travel to centers of knowledge and learning to gather esoteric information, valuables exchange among distant elite, long-distance travels by medicine persons, and vision and power quests.

Chaatsmith quotes Choctaw writer and intellectual LeAnne Howe, who visited the Ohio earthworks in 2011 and suggested that in the large open spaces at Newark, festivals might have hosted singing, feasting, games, races, meetings, storytelling, and trading. Did people come from far away to celebrate together?

On October 11, 2025, the Ohio History Connection hosted an official viewing of the standstill. It was the first time the Newark Octagon was fully open to the public during a standstill since its purpose was identified in 1982. About a hundred people watched as a spark grew and then the full orange moon rose through the trees. Must have been an amazing sight.

Project Takeaways

Two-thousand-year-old-lunar observatory in Ohio and connected to long-distance and long-term study of the sky? Of course the Octagon group at Newark belongs in Staring into Space.

While I was deep-diving into the research for this project, I discovered several compelling stories in Middle Woodland recent scholarly work that don't fit in with the rest of this tale, but might be of interest to you, dear reader.
  1. The Great Hopewell Road investigated primarily by U.S. archaeologist Brad Lepper (Magli and Lepper 2025) is a straight line — and I mean very straight indeed — route with parallel walled berms extending out from Newark to the southwest and connecting other monuments in the valley for a length perhaps as far as 90 km (50 mi).
  2. At the High Bank earthwork, and like Mississippian mounds of a later date (Sherwood and Kidder 2011), the mounds were built by exquisite layering different soils of varying colors and textures (Greber and Shane 2009).
  3. Christopher Carr (2021) describes evidence for ritual dramas, mortuary practices which reflect several narrative stories about the afterlife, how the dead change into birds or are led by bird guides up into the sky to cross the Milky Way. Fascinating stuff.

Figure Credits

  1. Octagon Earthworks, Avenue at Sunrise. 01/03/2021. Credit: Bradley T. Lepper. © Ohio History Connection. https://whc.unesco.org/en/list/1689/gallery/ CC: Attribution, No derivatives
  2. Serpent effigy of cut mica, Hopewell culture, Turner Group, Mound 4, Little Miami Valley, Ohio, 200 BC to 500 AD. Peabody Museum, Harvard University. Credit: Daderot. CC0 1.0 Universal Public Domain Dedication https://commons.wikimedia.org/w/index.php?curid=69527809
  3. Map illustrating some of the archaeologically-defined cultures sharing traits of the Hopewell Interaction Sphere. Image credit: Herb Roe, 2010. Creative Commons 3.0 https://commons.wikimedia.org/wiki/File:Hopewell_Exchange_Network_HRoe_2010.jpg
  4. Newark Works, Licking county, Ohio. Squier & Davis 1837-1847. Public domain. Found in Squier, E.G. and E. H. Davis. "Ancient Monuments of the Mississippi Valley." Contributions to Knowledge, Bartlett &Welford, 1848 1848. https://archive.org/details/ancientmonuments00squi/
  5. Map of the Newark Octagon as enshrined in the Hopewell Ceremonial Earthworks UNESCO World Heritage Site. Credit: UNESCO. Public domain https://commons.wikimedia.org/wiki/File:Octagon_Earthworks_Map_UNESCO.png
  6. Illustration of the full moon rise during the standstill of 2005, created by the University of Cincinnati's Center for the Electronic Reconstruction of Historic and Archaeological Sites (CERHAS). https://www.flickr.com/photos/fusion_of_horizons/5324545530/
  7. Flickr user György Soponyai spent a week creating a simulacrum of a lunar analemma over Budapest using Stellarium and Photoshop--analemmas are time-lapse illustrations of the movement of celestial objects. He published his results on Flickr under a Creative Commons license 2.0. https://www.flickr.com/photos/vanamonde81/49859483963
  8. A view of the Sept. 19, 2023 Hopewell Ceremonial Earthworks commemoration event area at the Mound City Group. NPS Photo / Tom Engberg.


Selected Sources

  • Atwater, Caleb. '"Description of Antiquities Discovered in the State of Ohio and Other Western States." Peabody Museum of Archaeology and Ethnology, Harvard University, 1973. Antiquities of the New World: Early Explorations in Archaelology.
  • Bernardini, Wesley. "Hopewell Geometric Earthworks: A Case Study in the Referential and Experiential Meaning of Monuments." Journal of Anthropological Archaeology, vol. 23, no. 3, 2004, pp. 331–56, doi: https://doi.org/10.1016/j.jaa.2004.06.001
  • Carr, Christopher. "More Souls in Flight: Ritual Dramas of Death Journeys through the above Realm(s) of Hopewellian and Adena Societies Beyond the Scioto." Being Scioto Hopewell: Ritual Drama and Personhood in Cross-Cultural Perspective, Springer International Publishing, 2021, pp. 593–659. https://doi.org/10.1007/978-3-030-44917-9_11
  • Chaatsmith, Marti L. "Singing at a Center of the Indian World: The Sai and Ohio Earthworks." American Indian Quarterly, vol. 37, no. 3, 2013, pp. 181–98, JSTOR, doi: https://dx.doi.org/10.5250/amerindiquar.37.3.0181
  • Garner, Sandra. "Reinterpretation of ‘Sacred Space’ at the Newark Earthworks and Serpent Mound: Settler Colonialism and Discourses of 'Sacred'." Review of International American Studies, vol. 16, no. 1, 2023, pp. 87–114, doi: https://dx.doi.org/10.31261/rias.13857
  • Greber, N'omi B. and Orrin C. Shane III. "Field Studies of the Octagon and Great Circle, High Bank Earthworks, Ross County, Ohio." In the Footprints of Squier and Davis: Archeological Fieldwork in Ross County, Ohio, edited by Mark J. Lynott, National Park Service, 2009, pp. 23–48.
  • Hancock, John E., editor. Hopewell Ceremonial Earthworks: Landscape Monuments of the Ancient Ohio Valley. Smithsonian Books, 2026.
  • Hancock, John E. and Bradley T. Lepper. "Earthen Architecture of the Ancient Ohio Valley." Terra 2022, edited by Leslie Rainer et al., Getty Publications, 2025, pp. 510–16. Proceedings of the 13th World Congress on Earthen Architectural Heritage, Santa Fe, New Mexico, USA, June 7-10, 2022, JSTOR, http://www.jstor.org/stable/jj.32155379.73
  • Hively, Ray and Robert Horn. "Geometry and Astronomy in Prehistoric Ohio." Journal for the History of Astronomy, vol. 13, no. 4, 1982, pp. S3–S20, https://ui.adsabs.harvard.edu/scan/manifest/1982JHAS...13....1H
  • --. "Hopewell Topography, Geometry, and Astronomy in the Hopewell Core." Encountering Hopewell in the Twenty-First Century, vol. 5, 2020, pp. 117–53.
  • --. "A New and Extended Case for Lunar (and Solar) Astronomy at the Newark Earthworks." Midcontinental Journal of Archaeology, vol. 38, no. 1, 2013, pp. 83–118, JSTOR, https://www.jstor.org/stable/26599875
  • --. "A Statistical Study of Lunar Alignments at the Newark Earthworks." Midcontinental Journal of Archaeology, vol. 31, no. 2, 2006, pp. 281–321, JSTOR, https://www.jstor.org/stable/41582324
  • Lepper, Brad. "The Great Hopewell Road: A Biased Assessment Thirty Years On." Journal of Ohio Archaeology, vol. 10, 2024, pp. 1–37.
  • Lynott, Mark J., editor. In the Footprints of Squier and Davis: Archeological Fieldwork in Ross County, Ohio, Special Report 5. National Park Service, 2009.
  • Magli, Giulio and Brad Lepper. "Going Straight in a Sacred Landscape: The Great Hopewell Road." Studies in Digital Heritage, vol. 9, no. 1, 2025, pp. 37–54, doi: https://dx.doi.org/10.14434/sdh.v9i1.40843
  • Marshall, James A. "Defining the Bounds of the Hopewell Core and Periphery Utilizing the Geometric Earthworks." Ohio Archaeologist, vol. 47, no. 4, 1997, pp. 24–32.
  • Noodin, Margaret. "Bundling the Day and Unraveling the Night." American Indian Quarterly, vol. 37, no. 3, 2013, pp. 237–40, JSTOR, doi: https://dx.doi.org/10.5250/amerindiquar.37.3.0237
  • Sherwood, Sarah C. and Tristram R. Kidder. "The Davincis of Dirt: Geoarchaeological Perspectives on Native American Mound Building in the Mississippi River Basin." Journal of Anthropological Archaeology, vol. 30, no. 1, 2011, pp. 69–87, doi: https://dx.doi.org/10.1016/j.jaa.2010.11.001
  • Sieg, Lauren and Jarrod Burks. "The Land between the Mounds: The Role of "Empty" Spaces in Ethe Hopewellian Environment." Hopewell Settlement Patterns, Subsistence, and Symbolic Landscapes, edited by A. Martin Byers and Dee Anne Wymer, University Press of Florida, 2010, pp. 56–71.
  • Thomas, Cyrus. "Report on the Mound Explorations of the Bureau of Ethnology." Annual Report of the Bureau of American Ethnology, 1894. https://archive.org/details/bureauofethnology00thomrich/
  • Thomas, Cyrus. The Circular, Square, and Octagonal Earthworks of Ohio. Government Printing Office, 1889. Smithsonian Institution. Bureau of Ethnology, J.W. Powell. https://archive.org/details/b30477633
  • Voros, Craig Matthew. "Myaamia Calendar Project Phase Ii: Lunar Calendar Calibration." Institute of Environmental Sciences, for Master of Environmental Science, Miami University, 2009. Advisor, Adolph M. Greenberg, https://rave.ohiolink.edu/etdc/view?acc_num=miami1240406619
  • Wright, Alice P. and Erika Loveland. "Ritualised Craft Production at the Hopewell Periphery: New Evidence from the Appalachian Summit." Antiquity, vol. 89, no. 343, 2015, pp. 137–53, doi: https://dx.doi.org/10.15184/aqy.2014.34

This article is part of the Staring into Space project.
Questions? Comments? Suggestions? Contact me at Email Screenshot