Almost everyone who visits the Octagon sites winds up asking: Why would anyone think of building a gigantic octagon? There is a logical answer, and it is rooted in traditions that were already thousands of years old. Shaman-midwives were building increasingly accurate calculators in order to more precisely understand the cosmic cycles of Grandmother Moon. This, in turn, would be expected to produce more accurate calendars for calculating the most fertile times of every woman’s monthly cycle, and for monitoring the stages of every pregnancy.
Among the ancient Ohio earthworks recently added to the UNESCO World Heritage List, the most befuddling are two very similar ones, both in the shape of gigantic irregular octagons. One, southeast of Chillicothe, is called the High Bank Octagon, probably built in the 1st century CE, and the other, probably built about two centuries later, is 58 miles to the northeast in Newark. The shapes of the two are completely congruent, but the Newark Octagon has dimensions exactly double those of High Bank.
It was discovered in the 1980s by the archaeoastronomers Ray Hively and Robert Horn that both of these octagons have the astounding feature of having their sides and gateways point to all eight of the moon’s maximum and minimum rise and set points over the moon’s long 18.61-year cycle. Who even knew that the moon had an 18.61-year cycle? Did you? The lunar alignments raise all sorts of questions about the identity and motives of the builders, but until now, the mental image has prevailed of wonkish male astronomy-math nerds who would take careful lunar measurements over the better part of their short adult lives and use the data to design complex and pointless geometrical structures. That idea can now be laid to rest.
It should have been taken as a big clue that the lunar spirit as seen by Algonquian descendants of the builders of High Bank and Newark, is female. The Shawnee call her Kokumthena (Our Grandmother) and have raised her to the status of a creator deity. The Ojibwe call her Nookomis Tibik Giizis (My Grandmother Night Light, i.e. Moon), and similarly in Cree, Nôhkom Kisiskwew. In all these terms, the root word for grandmother is kom or kum, which may derive from the name of the worshiped lunar deity in southern Siberia, from which the Algonquians derive – Umay, whose cult is extremely ancient. In all of these cases, the lunar spirit guides women’s cycles in time with the moon and is responsible for fertility and birth. In much of Siberia and Mongolia, women shaman-midwives are called some variation of Odagan, which comes from the Mongolian name of Umay.
Menstrual calendars, presumably made by shaman-midwives, are found from the south-Siberian Mal’ta-Buret’ Culture, near Lake Baikal, recorded on mammoth tusks and on female figurines, going back earlier than 15,000 years ago, which is before Algonquian ancestors left the Lake Baikal region (as confirmed by DNA lineages). Some of these calendars, including later ones made by the Okunev Culture, explicitly link the menstrual and lunar cycles.
Algonquians of the historic period also have linked these cycles through a shared Algonquian lunar calendar, comprised of 13 months of 28 days each, with each month called a “moon,” just as in Germanic languages including English. Algonquians also commonly used turtle shells as calendars, because North American turtle species have 13 central scutes or plates, and some species have 28 scutes around the edge. Part of the Algonquian midwifery math that becomes important is that an average pregnancy term was counted as ten months, or 280 days, since last onset of menstruation. The same average term is estimated by modern obstetrics and midwifery. (Equivalent to between 266 and 270 days from conception.)
That the ancient Adena mound-builders of the middle Ohio Valley, who were directly ancestral to the Shawnee and other Algonquian tribes, used similar if not the same turtle-shell calendars is made clear from an extraordinary artifact unearthed from the Cresap Mound in the 1950s. The destroyed Cresap Mound was part of the Adena Grave Creek archaeological complex on the banks of the Ohio River, twelve miles south of Wheeling, West Virginia. The artifact, shown above, is the stone tablet of a turtle, whose body is formed by a regular octagon.
This must be considered as a forerunner of the octagon earthworks at High Bank and Newark, with the octagon used as a symbol of the moon, its eight vertices pointing to the eight lunar maximum and minimum rise and set points. There is not a good dating of the Cresap turtle tablet, but it most likely dates to at least a couple centuries before the High Bank Octagon. (The Grave Creek Mound dates to approximately 200 BCE, roughly three centuries before High Bank.) At minimum, this shows that the Adena (the identical culture as what is mistakenly called “Hopewell” by some) were Algonquians (as confirmed by DNA analysis) and were using Algonquian turtle calendars of octagonal shape to model the lunar cycles, centuries before the large octagon earthworks were constructed.
This also suggests that the people engaging in this lunar tracking and calendar design were not male math nerds, but were actually female shaman-midwives, whose principal goal, like that of their Siberian ancestors, was to track the moon in order to better understand women’s menstrual and pregnancy timing, thought to be under the guidance of Grandmother Moon. To test this hypothesis, I decided to revisit what has been called “the astounding geometry” of the octagonal earthworks, to see if midwifery math is apparent.
A foundation for this reanalysis was laid by Hively and Horn and by the archaeologist Bill Romain, and I’ve also benefited from personal conversations with all three. The High Bank and Newark octagons are both matched by circular earthworks of nearly the same diameter, about 1054 feet, give or take a foot or two. These circles give insight into what the builders used as standard units of measure. Decades ago, Romain calculated what he thought was the Adena-Hopewell standard unit as 1/500th of the High Bank-Newark circle diameter, or very close to 25.3 inches. My own investigations support that calculation, and I call that unit the Adena cubit.
Rather oddly, no one had before calculated the lengths of each octagon side at either of the octagons. The wall lengths at each side have been measured and reported, but the walls are significantly shorter than the octagon sides, because there are open gateways at each octagon vertex. (Ok, ok, I was a math nerd in high school.) Using LiDAR images of the earthworks provided by my friend Sean Chaney, who operates the https://www.earthworks.site/ website, I calculated each octagon side at High Bank as 140 Adena cubits. 140 is equal to 5 months of 28 days each.
This immediately explains one motive for the building of the Newark Octagon, in which the dimensions of the High Bank octagon are doubled. I estimate the Octagon sides at Newark to be 590 feet long each, or 280 Adena cubits. 280 is 10 x 28, or the number of days in an average human pregnancy term. This is certainly a sacred geometry, but it’s not some generic sacred geometry – it’s the geometry of shaman-midwives, to whom the lunar calendar was of tremendous practical importance in devising fertility calendars and coaching pregnancies.
The Newark Octagon is actually constructed from eight regular triangles, each with outer side of 280 and angles of 45, 60, and 75 degrees as shown in my graphic above.
This implies that the Adena were measuring angles with precision, an impressive mathematical feat.
And it doesn’t stop there. The long lunar cycle of 18.61 years is comprised of approximately 240 monthly lunar cycles (the exact number varies and also depends on the accuracy of measurement of the monthly lunar cycle; also on whether lunar cycles or menstrual cycles are used for the calculation), or 24 average pregnancy terms. There are eight sides of the octagon; 8 is a factor of 24 and 240. This means that the octagon as a whole represents eight pregnancy terms or one third of the long lunar cycle that is tracked by the octagon – 24 pregnancy terms in total. It should be noted that most North American turtles have 24 scutes in their outer ring, not 28, though 28 has become a kind of accepted lore. The Adena probably used the correct figure of 24, representing the number of pregnancy terms in the long lunar cycle, not the number of days in a month.
And it doesn’t stop there. Just one mile southeast of the Newark Octagon is another larger circular earthwork called the Great Circle (seen above in the background picture).
The Great Circle is not entirely regular, but Hively and Horn estimated the diameter as 361.2 meters, which equals 1185.04 feet. They just didn’t recognize the significance of this number, and archaeologists have further obscured the significance by rounding the number to 1200 feet.
One big problem is that modern analysts keep talking about diameters. But every circle-maker knows that the way to make a circle is using the radius, not the diameter. Most Adena circles would have been made by staking a rope and tracing out the circle. The rope length is the radius, not the diameter. So the Newark Great Circle had a radius of about 592.52 feet. That is nearly the same as the octagon side length, which I measure as about 590 feet. Accounting for error margins, this means that the intended radius of the Great Circle was probably the same as the side length of the Octagon, both being 280 Adena cubits – an extremely important correspondence that has not been noted before.
By the way, we can now understand an anomaly of the standard Algonquian calendar. It puts each month at 28 days, but the actual synodic cycle of the moon (time from full moon to full moon) is 29.53 days, and the average menstrual cycle, cross-culturally, is the same, at 29.5 days. This means that the Algonquian calendar, touted as “natural,” will rapidly fall out of sync both with the moon and with the average woman’s cycle. The explanation is that the Algonquian calendar appears to have been designed by midwives, with the governing cycle being the 280-day 10-month average pregnancy term. The 28-day calendar month is set at one tenth of the pregnancy term, not in accord with the lunar monthly cycle.
Considering the Cresap turtle tablet and the High Bank Octagon as precursors to the Newark Octagon, it is now pretty clear what the Adena shaman-midwives were doing. They were building increasingly accurate calculators in order to more precisely understand the cosmic cycles of Grandmother Moon. This, in turn, would be expected to produce more accurate calendars for calculating the most fertile times of every woman’s monthly cycle, and for monitoring the stages of every pregnancy.
And that wasn’t any wonkish male mathematical obsession. It was a most practical and scientific endeavor, which now can be understood as not much a mystery.
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This article is written in honor of my mother Iris’s 91st birthday.
*Geoffrey Sea is an Ohio-based writer and historian, who has long studied the Ohio earthworks. He is the administrator of the Adena Core group on Facebook.
