YEAH. My new book is finally completed and published. Total 332 pages, 513 illustrations, 258 bibliography entries. If you want to know more about the Moundbuilder earthworks in south-central Ohio then you're going to love this oversized book, jam-packed with hundreds of illustrations. In this volume the latest LiDAR technology is combined with relational archaeology and archaeoastronomy to answer the questions of why the earthworks were built and how they were used by people two thousand years ago.
 Here's the link to order:
Figure 1. Artist's representation of the Aztalan site. Illustration by Herb Roe.
Aztalan is located on the Crawfish River, in Jefferson County, Wisconsin. Sometime between A.D. 1000 -  A.D. 1100, Mississippian people from the Cahokia region established a presence at Aztalan. In this and as archaeologist Thomas Zych (2013:13) has summarized, this presence was "coeval with an extant Late Woodland occupation."
Figure 2. Map of Aztalan published in 1855 by Increase A. Lapham (1855:Plate XXXIV). Note that Lapham oriented the map so that north is facing to the right.

Major features of Aztalan include several large mounds, a palisade, plaza, habitation area, and series of conical mounds.
Figure 3 (left). LiDAR image of Aztalan. (Mound C is a natural hill feature that was incorporated into the design of Aztalan. Mound D does not show-up very well in the LiDAR imagery. For purposes here, a rectangle showing Mound D has been added by the present author based on survey data provided by Zych (2013).
Figure 3 (right). Schematic plan of central Aztalan. Mound numbering following Lapham (1855). Drawing by Romain after Zych (2013:Figure 1.2).


Ceremonial Post Mound Group
We begin with the line of conical mounds just to the northwest of central Aztalan . In Figure 3 (above left), this group is labeled "Post Mound Group." These mounds were central to the layout of Aztalan. When explored by Lapham in the mid-1800s, there were more than 30 mounds in the group. Most have been plowed-down to where only about 10 are still visible.
Figure 4. View showing part of the Ceremonial Post Mound Group.
The Post Mound Group was explored by Lapham (1855) and Barrett (1933). Lapham (1885:48) reported finding human bones in one of the mounds located on Mound Street. From Lapham's description it is difficult to know if the mound he referenced was part of the Post Mound Group. In any event, a female burial was found in another mound - known as the Princess Mound. Excavated by Samuel A. Barrett (1933:241) the young woman was estimated as between 20 - 25 years of age at the time of her death. Her body appeared to have been wrapped in a bark covering, secured by three beaded belts wrapped around the bundle. 

Several mounds in the Post Mound Group were found to have a central dug pit (Barrett 1933:227-240). A broken section of a wooden post almost two feet in diameter was found in one mound pit - leading to the likely suggestion that the other pits were also used to support large posts.

James Scherz (1987:65) reports that the largest extant mound in this group (Mound C1 in Figure 5) was one of the mounds that likely held a ceremonial post; and from this mound, the winter solstice sunrise would have been visible over Christmas Hill, located about 2.3 kilometers to the southeast. My calculations corroborate that finding.

No radiocarbon dates have been obtained from the Post Mound Group; nor have diagnostic artifacts been found that clearly identify when these mounds were built. Based on similarities to other conical mound groups common to the Effigy Mound Culture area involving placement along ridge lines, I suspect that construction of the Post Mound Group mostly occurred during the Late Woodland period, perhaps supplemented by later Mississippian-era construction (if, for example, the Princess Mound burial is Mississippian in age).

Interesting to note is that the Post Mound Group is oriented to within about four degrees to Telfer Hill. Telfer Hill is a high hill situated about two kilometers northeast of the Post Mound Group. Located on the summit of Telfer Hill is a pyramid-shaped platform mound and an effigy mound said to resemble a headless man (Archaeological Conservancy 2014).

Figure 5. LiDAR contour map showing the Ceremonial Post Mound Group. One-half meter contour interval. White lines are parallel to each other and show how the trajectory of the mound group follows the ridge.

Figure 6. Three-dimensional LiDAR view of the Ceremonial Post Mound Group showing alignment of the mounds along the ridge.
Where discussion concerning the orientation of the Post Mound Group becomes relevant is in the finding that the four major mounds in central Aztalan are situated so they are parallel to the trajectory of the Post Mound Group. Figure 7 shows this relationship. In Figure 7 the blue line showing the trajectory of the Post Mound Group is parallel to the red line drawn between mounds A and B. Further, the white line between mounds C and D is parallel to both the red and blue lines. Thus all three lines are parallel to each other and to the ridge upon which the Post Mound Group is located.

If, for the sake of argument, the Post Mound Group predates main construction of central Aztalan, then the implication is that Mississippian builders incorporated the design principles of the local Late Woodland culture into their construction.

Figure 7. LiDAR view showing the parallel relationships between the trajectory of the Ceremonial Post Mound Group and mounds A - B, and C - D.  The red, white, and blue lines are parallel to each other.

Mound A
Mound A  (Figures 8 and 9) is also known as the Southwest Mound. This two tier flat-top pyramid mound is the largest mound at Aztalan. It currently measures about 16 feet in height and 185 feet by 130 feet at its base (Birmingham and Goldstein 2005:70). Notably, however, is that Barrett (1933: 225) reports: "we are told by some of the early settlers that special efforts were made in early times to level this pyramid in order to make it more easily tillable." Barrett (1933:231) suggested that the mound may have been reduced in height by as much as five feet by these efforts.

In any event, the mound takes advantage of a change in the terrain that rises from east to west (Figure 10). The significance of this will become evident later in the discussion.

Partial excavation revealed that Mound A was built in several stages. According to Barrett (1933:221), the base platform  revealed evidence of a centrally-located burned post. Further, Barrett (1933:221) discovered posthole evidence suggestive of a temple or house structure on top of the second mound level.

Figure 8. Profile view of Mound A looking to the north.
Figure 9. View of Mound A looking to the west.
Figure 10. Lidar view of Mound A showing how the mound takes advantage of a natural rise in terrain elevation thereby requiring less fill to create the base platform.
As to the orientation of Mound A, it is closely - but not precisely, oriented to the cardinal directions. Depending on which side one measures, the mound is skewed 2 - 3 degrees in a clockwise manner from the cardinal directions. Of course important to keep in mind is that over the years the mound has suffered erosion, plowing, partial excavation, and has been partially restored. 

As Figure 11 shows, viewed from Mound A, at about A.D. 1000 and for hundreds of years before and after, the moon would have appeared to set into the side of Signal Hill on the date of it's minimum north extreme. This event occurred every 18.6 years.

Signal Hill is located about 940 meters to the northwest of Mound A. The posited alignment presumes that the trees now partially blocking the view would not have been present when the site was in use by Mississippians. Note too that Signal Hill and Mound A have been plowed down over the years and thus the sightline between the two would have been higher and therefore more visible during Mississippian times. Figure12 shows the present line of sight between Mound A and Signal Hill.

Figure 11. LiDAR image showing moon minimum north set azimuth from Mound A into the side of Signal Hill.
Figure 12 (left). Three-dimensional LiDAR view showing Mound A - Signal Hill lunar alignment.
Figure 12 (right). Topographic profile from Mound A to Signal Hill. Line of sight indicated by dashed line.

Increasing the likelihood that the relationship between Mound A and Signal Hill was recognized by ancient Aztalan people is that a mound was originally situated on Signal Hill (Barrett 1933:250-252). Found by Barrett at the base of this mound were stones and mottled earth (Figure 13). Archaeologist Kurt Sampson has examined the curated items collected by Barrett from this mound. He reports that the stone is burned limestone (Sampson, personal communication 3-12-2015). If the burned limestone resulted from fires on top of Signal Hill, that would have allowed nighttime viewers situated at Mound A to clearly discern where the moon would set into Signal Hill. As further pointed out by Kurt Sampson (personal communication, 3-12-2015), the mottled color of the earth at the base of the mound may also have resulted from the action of fire.
Figure 13 (left). Barrett (1933:Figure 55) sketch of mound situated on top of Signal Hill.
Figure 13 (right). Barrett (1933:Figure 56) detail showing stone and mottled earth at base of the Signal Hill mound.

A second alignment associated with Mound A is a winter solstice sunrise alignment discovered by James P. Scherz (1987). This alignment extends from Mound A to a mound located on a ridge situated to the southeast, just across the Crawfish River. Scherz describes the target  mound as crescent-shaped. Unfortunately LiDAR resolution is not sufficient to confirm the shape of the mound. In any case, for the sake of convenience we can call this mound the  'Solstice Marker Mound' and the ridge, 'Sunrise Ridge.' Notably, there are additional mounds visible in the LiDAR along the edge of Sunrise Ridge (Figure 14). Several of these mounds are shown on Lapham's 1855 map of the area (Figure 15).

The Solstice Marker Mound is not silhouetted against the horizon. Rather, there is a higher ridge to the southeast of Sunrise Ridge that forms the visible horizon. Nevertheless, as pointed-out by Scherz (1987) and photographically documented (Scherz 1987:Fig. 4; Weier 1988) the sightline from Mound A to the winter solstice sunrise would have been in line with the Solstice Marker Mound on Sunrise Ridge. This relationship is shown below in Figure 16 (left and right).

Figure 14. LiDAR image showing winter solstice rise azimuth from Mound A.
Figure 15. Enlarged detail from Lapham (1855:Plate XXXV) showing mounds on Sunrise Ridge. Annotation added by present author.
Figure 16 (left). Topographic profile from Mound A along winter solstice sightline.
Figure 16 (right). Photograph of the winter solstice sunrise from Mound A. For this photograph a light was set-up by members of the Ancient Earthworks Society on one of the mounds situated on Sunrise Ridge. As can be seen, the winter solstice sunrise is in line with the light and therefore, the marker mound. Photograph by and used with permission of David Weier, Ancient Earthworks Society, Inc.

It is interesting that Mound A is located at the intersection of the moon's minimum north set azimuth and the winter solstice rise azimuth. The intersection of these two celestial azimuths positions Mound A in very specific location on the landscape.

Mound B
Mound B is also known as the Northwest Mound. Shown in Figure 17, the structure is a flat-topped, platform mound. Similar to Mound A, Mound B is also skewed a bit from the cardinal directions. Specifically the major axis of Mound B extends along an azimuth of about 003.5 degrees. The mound is about nine feet high and was built in three stages. Found at the second stage of construction were the remains of a Spirit House (my term rather than "charnel house") (Rowe 1958). Situated within the Spirit House were the remains of 11 people - men and women. According to Birmingham and Goldstein (2005:Figure 4.20b) the house structure "seems oriented southeast to the winter solstice sunrise and northwest to the summer solstice sunset."
Figure 17. View of Mound B.
As Figure 18 shows, viewed from Mound B, at about A.D. 1000 and for hundreds of years before and after, the moon would have appeared to rise over Christmas Hill on the date of its minimum south extreme. Christmas Hill is located about 2.2 kilometers to the southeast of Mound B. A solitary mound surveyed and mapped by James Scherz (1990:Fig. 2) is situated on top of Christmas Hill. Figure 19 (left and right) shows the line of sight between Mound B and Christmas Hill.
Figure 18. LiDAR image showing moon minimum south rise from Mound B over Christmas Hill.

Figure 19 (left). Three-dimensional view of moon minimum south rise sightline from Mound B over Christmas Hill.
Figure 19 (right). Topographic profile from Mound B to Christmas Hill.

What makes the lunar minimum south rise sightline from Mound B over Christmas Hill of special interest is that it is the counterpart to the lunar minimum north set sightline found for Mound A.

Further linking mounds A and B is that, as shown by Figure 7, mounds A and B are situated on a line that extends parallel to the line of ceremonial post mounds. This serves to fix the location for Mound B at the intersection of the moon's minimum south rise azimuth and the line that connects mounds A and B. Thus the location for Mound B was established by reference to celestial and terrestrial azimuths.

Mound C
Mound C is a small natural knoll that appears integrated into the design of Aztalan.  Because the knoll resembles a mound it may have been considered as such by the ancient Aztalan people. In other words, knolls, mounds, and hills may have been thought-of as metaphorical variations of an underlying concept. This notion is supported by the manner in which the knoll is incorporated into the parallel-line design of the site as shown in Figure 7. Since by its nature the knoll (i.e. Mound C) predates Mound D, it seems that Mound D was intentionally situated where it is in order to build upon the parallel-line design feature exhibited by the relationship between the Post Mound Group and mounds A-B. Of interest is that exploration by Barrett (1933:143-144) found a flexed burial in Mound C at a depth of 30 inches below the mound surface.

Figure 20 shows Mound C as it appears today. A small kiosk is now situated on the top of the mound. 
Figure 20. View of Mound C from the west.
In addition to its resemblance to a man-made mound what may have made Mound C important to the Aztalan people was its directional relationship to Mound A. Specifically, Mound C is directly east of Mound A (also see Scherz 1987:Fig. 3). Thus mounds A and C establish the cardinal directions of east-west. Figure 21 shows this relationship (note 1).
Figure 21. LiDAR contour map (1/2 meter contour interval) showing directional relationship between mounds A and B.

Mound D
Mound D is also known as the Northeast Mound. The mound was probably never very high and today it is difficult to recognize in the LiDAR imagery. Birmingham and Goldstein (2005:62) suggest that the mound was about five feet high at its east end. As shown by Lapham (Figure 22 below) the mound sloped inward toward the interior plaza. Mound D appears to have been built as a "single event" albeit with multiple short term construction episodes resulting in mound stages (Zych 2013:100, 183). Exploration of Mound D found that a large house or temple structure was located on top of the mound (Goldstein and Freeman 1997). According to archaeologist Tom Zych (2013:180) ceramics recovered from within Mound D included those representative of Late Woodland local populations and the Mississippian occupation. This suggests that the Mound D location was considered special by people of both traditions - with that recognition honored and elaborated upon by the more recently arrived, Mississippian peoples.
Figure 22. Enlarged detail from Lapham (1855:Plate XXXIV) showing Mound D. North arrow added by present author.

Viewed from Mound D, at about A.D. 1000 the moon would have been seen rising over Christmas Hill on the date of its minimum south extreme. Figure 23 shows this relationship. Figure 24 shows a close-up of Christmas Hill. The exact point on Christmas Hill where the moon rose (center of moon tangency) is about 120 meters south of the intersection point for the Mound B alignment. Basically the Mound D alignment is a repeat of the Mound B alignment.
Figure 23. LiDAR image showing moon minimum south rise from Mound D over Christmas Hill.
Figure 24. Close-up LiDAR view of Christmas Hill showing lunar sightline intersection points viewed from mound B and D.
Where things become interesting is in another alignment involving Mound D. This alignment extends from mound C2 in the Post Mound Group, through the center of Mound B, to the center of Mound D. Figure 25 shows the relationship. Mound D is thus located at the intersection of a celestial alignment to the moon and two terrestrial alignments - one involving a parallel relationship to mounds A-B, and the second involving an alignment to Mound C2 through Mound B.
Figure 25. Blue line shows the linear relationship between mounds C2, B, and D.

There are several interesting observations that can be made about what has been presented. To begin with, there is an internal logic evident in the placement of each major mound on the landscape. Clearly the locations for mounds A, B, C, and D reflect a sophisticated combination of celestial and terrestrial alignments. In particular, each of these mounds is situated at the intersection of celestial and terrestrial azimuths. The repeated use of this design technique at Aztalan suggests that the use of intersecting azimuths to position the earthworks was quite deliberate. Parenthetically, the use of intersecting azimuths to position earthworks appears to be common throughout the Eastern Woodlands.

Second, the site appears to incorporate both local Late Woodland and Mississippian culture attributes. In particular, if the Post Mound Group and elements of Mound D are of the indigenous Late Woodland culture, then the orientation of mounds A, B, and C - presumably built by Mississippian peoples, demonstrates this assimilation. In this regard, the lunar alignments documented for mounds A, B, and D come as no surprise given similar lunar alignments posited for Cahokia (Romain 2015) and other Cahokia-influenced sites such as Emerald (Pauketat 2013).

It is interesting that mounds A and C are built on natural knolls or ridges. So too Signal Hill and Sunrise Ridge are hill features. Notable in each case is that these natural features are enhanced by man-made mounds. From this it follows that the natural features underlying the mounds are by themselves, variously aligned to celestial events. Recognition of this underlying alignment of earth features to celestial events may have - at least in part, played a role in what made the location for Aztalan special in the first place.

There are other alignments at Aztalan. And, I have not even begun to touch upon the geometry of the site, or how the site incorporates the same unit of measurement as found at Cahokia. To include these matters would require a much longer blog page - and there are limits. That said, I hope I have provided sufficient information about Aztalan to stir the imagination and a sense of awe with respect to the accomplishments of the Native Americans who built this fascinating site.

What makes Aztalan special to me is how everything at Aztalan is entangled and connected in a relational web involving earth, sun, moon, mounds, and people - living and dead. Special people lived on special mounds, dead people were buried within. The Aztalan mounds  were of the earth, but at the same time, through their alignments,  they connected to the sun and moon and cosmic cycles. The past was linked to the Aztalan present though the incorporation of older mounds into the design of a Mississippian town. In these things, everything was inter-related; everything was connected.

1. This is not the same as an equinox alignment. This is because the sun rise and sets at the exact azimuths of 090 and 270 degrees only when the horizon is 0.00 degrees in elevation. As the distant horizon elevation increases, the rising and setting azimuths for the sun change accordingly. At mound A and C, the horizon elevations are not 0 degrees - thus the sun's rising and setting azimuths are not 90 and 270 degrees.

I wish to thank David Weier for sharing his knowledge of Aztalan with me. Thanks also to Dave Weier and the Ancient Earthworks Society, Inc. for the winter solstice photograph. Many thanks  to Gary Maier for sending me early reports from the Journal of the Ancient Earthworks Society, Inc.

Special thanks to Douglas Norgord for directing me to the Wisconsin LiDAR

I am greatly indebted to Kurt Sampson for answering my many questions about Aztalan. Thank you Kurt.

The work of Dr. James P. Scherz has figured importantly in the present assessment. Jim Scherz has worked tirelessly to survey and document the many
mound sites in Wisconsin. Thank you Jim Scherz for your many contributions.

I am solely responsible for the contents of this article.

Archaeological Conservancy
2014 Telfer Mounds (Wisconsin). Electronic document,, accessed March 17, 2015.

Barrett, Samuel A.
1933  Ancient Aztalan. Museum of the City of Milwaukee, Bulletin 13.

Birmingham, Robert A., and Lynne G. Goldstein
2005  Aztalan: Mysteries of an Ancient Indian Town. Wisconsin Historical Society Press, Madison.

Goldstein, Lynne, and Joan Freeman
1997  Aztalan: A Middle Mississippian Village. Wisconsin Archeologist 79(1+2):223-248.

Lapham, Increase A.
1855  The Antiquities of Wisconsin, As Surveyed and Described. Reprinted in 2001, with a foreword by Robert A. Birmingham and introduction by Robert P. Nurre. University of Wisconsin Press, Madison.

Pauketat, Timothy R.
2013  An Archaeology of the Cosmos: Rethinking Agency and Religion in Ancient America. Routledge, London.

Romain, William F.
2015  Moonwatchers
of Cahokia. In Medieval Mississippians: The Cahokian World, edited by Timothy R. Pauketat and Susan M. Alt, pp. 32-41. School for Advanced Research Press, Santa Fe.    

Rowe, Chandler W.
1958  A Crematorium at Aztalan. Wisconsin Archeologist 39(1):101-110.

Scherz, James P.
1987  New Surveys of Indian Mound Layout. Wisconsin Academy Review, March 1987:63-66.

1990  Annex E. Journal of the Ancient Earthworks Society  3:E1-E9.

Weier, Da
vid D.
1988  Major Astronomical Solstice and Equinox Alignments at Aztalan. Reprinted 2012 in Aztalan: Selections from The Journal of the Ancient Earthworks Society, Inc.

Zych, Thomas J.
2013  The Construction of a Mound and a New Community: An Analysis of the Ceramic and Feature Assemblages from the Northeast Mound at the Aztalan Site. Master of Science thesis, University of Wisconsin-Milwaukee.

The folks at Cahokia have a great line-up for their Winter Lecture Series. Hope to see you there!

Cahokia Mounds State Historic Site


Gregory Vogel, PhD, SIU Edwardsville

"The Archaeology of Disaster"

Dr. Vogel will be addressing the prehistory and history of major disasters--fire, flood, famine, war, plague, and earthquake--that have left distinctive signatures in the archaeological record, and Illinois has  seen its share of these.  We are still adapting today to events that have a history long beyond living memory. Greg will be doing this presentation as a presenter for the Road Scholars program of the Illinois Humanities Council.


Susan Alt, PhD, Indiana University

"Discovering Cahokia's Religion: Recent Research and New Interpretations of the Emerald Mound Complex, Lebanon, Illinois"

Dr. Alt has been working in the uplands east of Cahokia and has been running a joint field school with her husband, Dr. Timothy Pauketat, from the University of Illinois. They have spent the last few years excavating at the Emerald Mound site north of Lebanon, IL where they have found evidence of numerous structures that may have served as "shrines" and others as temporary living quarters for travelers following prepared roadways to and from Cahokia, some coming from great distances. They believe Emerald was a pilgrimage site associated with a new religion developing at Cahokia and that the site has lunar alignments.  She will discuss the results of their excavations and new interpretations of how this site functioned.


William Romain, PhD, The Ancient Earthworks Project

"Ancient Skywatchers of the Eastern Woodlands"

Dr. Romain's presentation chronicles a five-thousand year-old tradition of Native American skywatching. Using state-of-the-art LiDAR imagery and archaeoastronomic assessment protocols, he documents celestial alignments of representative sites from the Archaic, Woodland, and Mississippian periods. This includes the sites of Watson Brake, Poverty Point, Newark Earthworks, Mound City, Serpent Mound, Angel Mounds, and Moundville. Of special interest, the great city of Cahokia is shown to be designed using nested squares, a special unit of length, and alignments to the moon.  He also explores certain design principles held in common across the region and significant trends through time.


Figure1. View of the Serpent Mound tail illuminated by candles on 12-21-2014.
It was a spectacular evening as more than 1,000 people gathered for the annual candle lighting ceremony at Serpent Mound. Old friends met and new friends were made as people waited in breathless anticipation of sunset. As dusk turned to dark, the candles were lit and we watched - united in appreciation of the scene unfolding before us as the sun sank into the western horizon. In our experience of this event we knew that this celestial turning point marked the beginning of a new year - a year that promises hope and renewed life.

Figure 2. Photos of some of the people who gathered at Serpent Mound for the solstice candle lighting. Photos courtesy of Jeff Wilson and Bill Jordan.

Figure 3. View of the Adena conical burial mound at winter solstice sunrise. Photo courtesy of Thomas T. Johnson.
The conical burial mound was excavated in the late 1800s by Frederic W. Putnam of Harvard University. The mound was found to contain several burials. The central burial was an adult male with his head oriented to the east. Among the many items found in the mound were flint and ground stone implements, pottery sherds, pieces of fresh water clam shell,  burned bone, and a copper plate. Based on diagnostic findings the conical burial mound is attributed to the so-called Adena people.

The conical burial mound is an integral part of the Serpent Mound earthwork complex.

The burial mound is directly associated with the serpent effigy and the winter solstice sunset in the following way.

First, with reference to Figure 4 below, the LiDAR-measured distance (line A-B) between the apex of the oval embankment and center of the conical burial mound is 1,178 feet +/- ca. 2 ft. The significance of the 1,178-foot length is that it is found at other Moundbuilder earthwork sites. The diameters of the Newark Great Circle and Shriver Circle near Mound City, for example, are each 1,178 feet in length.

Second, the orthogonal (or perpendicular) of the 1,178-foot line is oriented to the winter solstice sunset to within two-tenths of one degree. (The 237.2-degree azimuth value takes into account distant horizon elevation, refraction, lower limb tangency, latitude, and 0 A.D. date +/- 200 years.)

Figure 4. LiDAR image of the Serpent Mound park.

Notably, the 1,178-foot length is derived from the Hopewell Measurement Unit (otherwise known as the HMU) of 1,054 feet. The 1,054-foot length (as well as greater and lesser multiples of that length) is found in many Adena-Hopewell earthworks including the Newark Octagon and Observatory Circle, Mound City, Hopeton, Baum, Shriver, and others. 

Figure 5 shows examples of the 1,054-foot length and how the 1,178-foot length is related to the HMU.
Fig. 5. LiDAR images of the Newark Octagon and Observatory Circle and Newark Great Circle showing how the HMU is incorporated and how the 1,178-foot length is derived.

Given the above, I believe several conclusions can be reasonably drawn: 

1) the serpent effigy, conical burial mound, and other ancient features in the park were likely intended by the Moundbuilders to comprise an integrated site complex. 

If this is true then, physical and visual barriers that divide the area - such as the one currently being planted and grown at Serpent Mound are inappropriate.

2) the linear and astronomic relationships between the serpent effigy and conical burial mound suggest that these relationships were not only intentional, but that their construction was likely contemporaneous, or very nearly so. Certainly that is the simplest explanation. If that was the case, then this provides further support for the recent finding that Serpent Mound was built during the Early Woodland period (see blog page elsewhere on this website concerning the new radiocarbon dates). 

3) the alignment data shown here suggest that winter solstice observations were part of the Ancient Ones understandings relative to Serpent Mound. Moreover and based on the relationship of the conical mound to the winter solstice, it seems likely that burial ceremonies, ancestor memorial events, world renewal ceremonies, and other activities may have been timed to celestial events - to include the winter solstice. If that was the case, then it is entirely fitting and proper that solstice celebrations should continue at Serpent Mound in recognition and in honor of those who built this world-class effigy. 

The Serpent Mound winter solstice candle lighting event has been a local tradition for a decade. Many people contribute to its success. Mostly, however, the event is the result of the hard work and dedication donated by members of the Friends of Serpent Mound. FOSM is comprised of individuals, organizations, and businesses dedicated to the preservation, protection, and promotion of Serpent Mound. For more information see the Friends of Serpent Mound website ( and Facebook page (http://www.facebook/groups/friendsofserpentmound/).

Figure 1. Survey map (Romain 1987) of Serpent Mound superimposed over LiDAR image. Image by William F. Romain.

Located in the rural countryside of Adams County, in southern Ohio, USA, Serpent Mound is probably the best-known and most widely-recognized prehistoric effigy mound in the world (Figures 1 and 2). For many people, Serpent Mound is a sacred site.
Figure 2. Aerial view of Serpent Mound. Photo by William F. Romain.

Given the significance of Serpent Mound, it is of considerable interest to know who built it and when. Recent investigations reveal that, contrary to an earlier report by Fletcher, et al. (1996), Serpent Mound was probably not built by people of the Fort Ancient culture - at about  A.D. 1070. But rather, was built more than 2,000 years ago - during the Early Woodland (Adena) period, around 321 B.C. (OxCal 2-sigma 381-44 B.C.).

The new findings are reported in detail in the peer-reviewed, Journal of Archaeological Science. An on-line, pay-for-view version of the article (for which the authors do not receive compensation) is available at:

The article is titled:
A New Multistage Construction Chronology for the Great Serpent Mound, USA"  and is co-authored by Edward W. Herrmann, G. William Monaghan, William F. Romain, Timothy M. Schilling, Jarrod Burks, Karen L. Leone, Matthew P. Purtill, and Alan C. Tonetti.

The following discussion is intended only as a brief summary of findings. Interested persons are encouraged to read the full report for a more thorough discussion.

In 2010, The Serpent Mound Project was initiated by William F. Romain. The objectives of The Project were to bring non-invasive and minimally invasive technology to bear on questions of who built the Serpent Mound, when, how, and why. Toward this end, a team of subject matter experts was assembled and pursuant to permits issued by the Ohio Historical Society, investigations were begun. Investigations included: geodetic survey, LiDAR analyses, hand coring, GeoProbe coring, magnetic gradiometer survey, electrical resistivity survey, ground penetrating radar, and limited excavation of a previously undocumented feature at the neck of the effigy. The discussion presented here is focused on the results of our GeoProbe coring work and the new radiocarbon dates. Details concerning our other work will be presented in a forthcoming edited book titled "Serpent Mound Revealed: Context, Archaeology, and Meaning."

GeoProbe Coring

Coring operations were done using a GeoProbe Model 54TR during April and September of 2011. The GeoProbe 54TR is a small John Deere tractor modified to include the DT-21 sampling system. The DT-21 sampling device works by hydraulically driving a core casing and contained sampling tube, into the ground. The core casing prevents the bore hole from collapsing. The soil sample is collected in the soil tube as the casing is driven into the ground. The sample tube is about 2.9 cm (1.1 in) in diameter. Core casings are 1.2 meters (4 ft) in length. Depending on the depth to be sampled, additional core casings are added.

Coring proceeded at 18 locations along the spine of the effigy. Figure 3 shows these locations. The locations were selected with consideration given to maximization of potential information, while avoiding delicate areas such as the oval and tail. Locations for each core were documented by total station measurements tied to a permanent benchmark located near the tail of the effigy.

Figure 3. Coring locations with associated radiocarbon dates. Figure by G. William Monaghan, inset mag image by Jarrod Burks. Reprinted from Journal of Archaeological Science, 50 (2014), Herrmann, et al. "A New Multistage Construction Chronology for the Great Serpent Mound, USA" with permission from Elsevier.


Cores were retrieved as continuous samples in closed tubes. Upon completion of coring, each hole was filled with bentonite to prevent erosion. The cores were analyzed by Bill Monaghan at the Glenn A. Black Laboratory of Archaeology, Indiana University, Bloomington. Cores were examined for color, texture, and other variables, as well as for organic substances suitable for radiocarbon dating and cultural inclusions.

From the 18 cores, a total of 9 soil samples containing possible charcoal were recovered from 5 cores. In all cases, Monaghan was able to clearly distinguish between layers of mound fill, the bottom of the mound, and submound paleosols. Figure 4 shows profiles of the cores that yielded datable samples. In Figure 4, m
ound fill is indicated by light gray; while the bottom of the mound is shown by the thick black line. According to Monaghan (2014:Figure 3 caption), "The submound paleosol was clear in all cores....[and] mound fill units are separated by clear abrupt contacts between units." Importantly, and as Figure 3 shows, the locations for the five cores - from which radiocarbon dates were obtained, come from widely separated areas along the length of the effigy.

As shown by Figure 4, four of the dated samples are from the Ab horizon or ZOD (Zone of Disturbance) that marks the base of the mound. The other three samples are from mound fill situated above the planar mound base.

Figure 4. Diagram showing core profiles and locations for dated samples. All dates are calibrated. Soil horizons as labeled. Figure by G. William Monaghan. Reprinted from Journal of Archaeological Science, 50 (2014), Herrmann, et al. "A New Multistage Construction Chronology for the Great Serpent Mound, USA" with permission from Elsevier.

After retrieval of the samples and analysis by Monaghan, they were provided to paleoethnobotanist, Karen L. Leone for additional assessment. Of the 9 recovered samples, Leone identified 7 samples that contained flecks of wood charcoal. None of the wood charcoal was of sufficient quantity to identify to the species level.

The 7 remaining samples were sent to Beta Analytic, Inc. of Miami, Florida for AMS radiocarbon dating. Due to the relatively small size of the charcoal flecks mixed into the soil matrices, the samples were processed as organic bulk sediments and dating proceeded in accordance with standard protocols. Radiocarbon dating results were forwarded to Tim Schilling - who, along with Bill Monaghan and Ed Herrmann, performed the OxCal analysis shown below in Figure 5.

Results of the OxCal analysis indicate that the Serpent Mound was likely constructed sometime between 381 B.C. - 44 B.C. (with a 95.4% probability). As Table 1 shows, the median calibrated age for Serpent Mound based on our data is 321 B.C.

Table 1 shows that our samples range in age from 639 - 303 B.C. (combined 95.4% probability range of 808 - 116 B.C.). This represents a ~350 year spread. If, however, the two inconsistent ages (Beta 337162 and Beta 337166) are discounted, then the range is even tighter. The Beta 337162 and Beta 337166 samples are 200-300 years older than the median ages from the ZOD; and as Figure 4 shows, they derive from mound fill that is 10-20 cm above the mound base. This age discrepancy is probably the result of charcoal deposited in submound Ab horizons during pre-mound occupations - which was then incorporated into the mound fill when Serpent Mound was built.

In any event, none of the median ages reported from any of our contexts within Serpent Mound are younger than 303 BC. In particular, no Fort Ancient charcoal was found in the sampled mound fill, or at the base of Serpent Mound. If the effigy was built by anyone later than Adena-era people, then one might expect to find some evidence of that in the way of organic materials or charcoal at the base. Such was not the case, however. If someone other than Early Woodland (i.e., Adena) people built the Serpent Mound, they were very fastidious in their work and left no trace at the foundation level. 

Table 1. All radiocarbon dates from Serpent Mound to include Fletcher, et al. 1996. Table by Edward Herrmann and G. William Monaghan. Reprinted from Journal of Archaeological Science, 50 (2014), Herrmann, et al. "A New Multistage Construction Chronology for the Great Serpent Mound, USA" with permission from Elsevier.

Figure 5. Diagram showing all radiocarbon dating results. OxCal refers to the calibration program and model used to plot the date ranges. Beta numbers refer to the laboratory and sample number. Figure by G. William Monaghan. Reprinted from Journal of Archaeological Science, 50 (2014), Herrmann, et al. "A New Multistage Construction Chronology for the Great Serpent Mound, USA" with permission from Elsevier.

What About the Fort Ancient Dates?

If Serpent Mound was built during the Early Woodland period, then the question that remains unanswered is: How do we account for the later - i.e., A.D. 1070, Fort Ancient dates obtained by Fletcher, et al. (1996)?

To answer that, we need to re-visit the modern history of the site.

As readers may know, in the late 1800s, Serpent Mound was saved from destruction through its purchase by
Frederic W. Putnam of Harvard University and the ladies of Boston.  Subsequent to that purchase, Putnam partially restored the effigy and created the Serpent Mound Park. During the course of his work, Putnam cut several exploratory trenches through the effigy. Mostly, however, what Putnam did was restore the effigy to its presumed original height by placing dirt that had washed down from the mound and accumulated along its edges, back up onto the surface of the effigy.

No further exploration into the effigy was done after Putnam's work - until the early 1990s, when Fletcher, et al. (1996) conducted their research at the site.

In 1991, the Fletcher team located and opened one of Putnam's back-filled trenches, expanded the lateral extent of that trench into a non-Putnam back-filled section of the effigy, and from that area, secured charcoal for two radiocarbon samples. A third sample was recovered earlier by hand coring.

Two of the three dates that the Fletcher team recovered are identical – i.e., cal A.D. 1070 ± 70 (Fletcher, et al. 1996:133). The third sample obtained from the hand core came from a depth of 132 cm - well-below the planar surface of the mound. That sample dated to cal 970 B.C. Based on the A.D. 1070 dates and an iconographic interpretation for the head of the effigy, Fletcher, et al. (1996:105) proposed that Serpent Mound was built during the “Late Prehistoric” by people of the Fort Ancient culture.

The Fletcher, et al (1996) conclusion that Serpent Mound was built during the Late Prehistoric differs from the findings of the present investigation. We believe, however, that the 1,400-year difference between an Early Woodland and Late Prehistoric construction date for the effigy can be accounted for.

Specifically, it is suggested that the conflicting sets of dates can be reconciled if Serpent Mound was constructed during the Early Woodland and then later modified. In this scenario, initial mound construction occurred during the Early Woodland (Adena) period about 2,300 years ago, followed by a renovation or repair episode in the area of convolution # 3 about 1,400 years later during the Late Prehistoric (Fort Ancient) period. The posited repair by Fort Ancient people would account for the Late Prehistoric-dated charcoal that was found in convolution # 3 by the Fletcher team.

There are several lines of evidence that support this scenario.

The location of Serpent Mound on a karst-affected promontory makes areas of the effigy susceptible to erosion as well as sinkhole subsidence. Damage to portions of the mound extensive enough to require repairs would not be surprising given the effigy's relatively low, pre-restoration height (generally ≤1 m high immediately preceding Putnam's restoration per early photos), the antiquity of initial construction, and the effigy's ridge-top location amid gullies and karst topography.

More specifically, convolution # 3 - which again, is where the Fletcher-Putnam trench was placed, is located at the head of the largest and deepest gully draining the Serpent area (Figure 6). At this location, however, the drainage of water from the promontory into the gully is blocked by the Serpent. Today, the Serpent's body is built-up - as the result of Putnam's restoration. We suspect, however, that over the course of 1,400 years between the time of Adena construction and Fort Ancient occupation, water, caught inside of convolution # 3 eventually and periodically eroded its way across and through the effigy as it sought to find its way downslope via the gully.

Even today, after a moderate rain, it is clear that the built-up convolution # 3 blocks drainage (Figure 7). Eventual erosion of the Serpent's body at this location seems inevitable.
Indeed, even with the height of the effigy built-up as it is today, one can see from Figure 7 that all it would take is one or two really serious rain events (sometime over the course of more than one thousand years)  to washout convolution # 3 in the area of the Fletcher-Putnam trench.

In short, convolution # 3 has probably long been subject to erosion and likely needed occasional repair due to its location at the head of a major gully.

Figure 6. LiDAR-contour map of Serpent Mound showing location of Fletcher-Putnam trench relative to erosional gully. Figure by William F. Romain.
Figure 7. Water pooling inside convolution # 3 where the Fletcher-Putnam trench was cut. Photo by William F. Romain.

2. The soil stratigraphy of the effigy at convolution # 3 is different from other areas of the Serpent. As geoarchaeologist Ed Herrmann (Herrman, et al. 2015) explains: "The Fort Ancient-age charcoal occurs only in the Fletcher, et al. (1996) trench, whose morphological and depositional contexts are atypical compared to the core samples we obtained. Our cores show that a well-developed, generally continuous paleosol underlies most of Serpent Mound. This paleosol is absent, however, in the Fletcher trench (Fletcher, et al. 1996:121-122, Figure 1). LiDAR and core data also show the mound is typically ~100 cm thick and sometimes directly underlain by a ZOD [Zone of Disturbance], which incorporated the pre-mound Ab-horizon during mound construction. However, the western end of convolution 3, where the Fletcher trench was placed is different. Not only are the submound paleosol and ZOD absent and the mound only ~50 cm thick, but at that location, the mound blocks downslope surface drainage from a depression situated on the inside of convolution 3."

Further, Herrmann (Herrman, et al. 2015) explain,
"Evidence of erosion and re-deposition within in this part of the mound is provided by the age of charcoal buried 70 cm below the Fort Ancient-age mound fill in the Fletcher trench. The age and depth of the charcoal (2920 BP, 95.4% probability 1368-925 BC, BETA 47212; Table 9.1) led Fletcher, et al. (1996:132-133) to conclude that it was related to a previous Late Archaic occupation and was 'carried to the lower depth by bioturbation or some other mode of transport.' We agree with this; but further suggest that the 'other mode of transport' was probably long-term erosion and re-deposition processes associated with gully formation. Based on the age of the buried charcoal, gully formation and erosion were ongoing processes. Erosion extensive enough to completely remove the original (Adena) mound fill and the upper part of the paleosol is consistent with the lack of a submound Ab/Eb horizons in the Fletcher/Putnam trench. That substantial erosion occurred at or near the Fletcher/Putman trench, at the apex of the convolution is further indicated by the absence of a submound paleosol [color added for emphasis]. As might be expected, the long convolution sections that extend along the same trajectory as the erosional gully were apparently not significantly altered by erosion."
3. Yet another line of evidence in support of the hypothesis that the effigy was repaired at convolution # 3 is the discovery of at least one other episode of prehistoric mound alteration. As Figure 3 shows, magnetic gradiometer survey by Jarrod Burks found evidence for what might be called a 'stealth' or 'abandoned' convolution at the neck of the Serpent. This feature is not visible on the surface by naked-eye, or in LiDAR imagery. What is left of the feature is situated below the present ground surface - but still detectable by magnetometer survey. Based on the superimposition of the present neck embankment over the 'stealth' coil, as well as the presence of Late Archaic artifacts recovered from our limited excavation into and across the stealth coil, it appears that this feature was probably built very early on, and subsequently erased from the surface, with the new neck configuration then built.

Given that at least one episode of prehistoric modification was made to the effigy, there is no reason to think that another episode - this one involving repair at convolution # 3 could not also have been made.

It is possible that some people will argue that what we dated was mound fill and that mound fill could come from anywhere and date to anytime. Such a representation, however, would not be accurate. As the data show, in no less than four instances, we did not date mound fill - but rather, charcoal situated in the Ab horizon, or Zone of Disturbance, at the very base of the effigy.

The question then becomes, 'what do the dates obtained from the Ab horizon or Zone of Disturbance represent relative to time of construction?' The matter is complicated; but basically can be summarized thusly:
"Our approach to resolving when Serpent Mound was first built is similar to that commonly used to date paleosols, which assumes that the time of paleosol burial is approximated by the youngest ages found (Herrmann, et al. 2014:121)." Following upon that with reference to Serpent Mound, "The distribution of ages...strongly suggest that the submound paleosol was more likely buried during an Adena construction" (Herrmann, et al. 2014:122). For further details and source documentation on this approach the reader is encouraged to review pages 121-122 of the JAS article.

In any case, it is again worth emphasizing
that no charcoal or other organic materials dating to the Late Prehistoric period were found at the base of the effigy. One might expect that if someone other than Adena people built the effigy, some evidence of their presence at the foundation level of the effigy would have been found in no less than 18 core samples. The lack of Fort Ancient-dated charcoal or organic materials at the base of the effigy is strong evidence that that culture was not responsible for construction of Serpent Mound. Moreover, the radiocarbon dates we obtained are internally consistent within a fairly narrow range of several hundred years.

The idea that Serpent Mound was built by people of the Adena culture is not new. Early-on, and based on his excavations, Putnam (1890) recognized that two different people occupied the Serpent Mound area during two different time periods. The terms Adena and Fort Ancient had not yet been applied to Moundbuilder peoples. However, Putnam - probably the most authoritative of all Serpent Mound investigators, attributed the effigy to the earlier of the two peoples he recognized. Likewise, Emerson Greenman (1934) (former Curator of Archaeology for the Ohio Historical Society), and William S. Webb and Charles E. Snow (1945:341), and Webb and Baby (1957:106) (archaeologists who literally wrote the books on Adena) also attributed Serpent Mound to the Adena.

Contributing to assessment of the Serpent Mound as Adena was the cultural affiliation of the large conical mound situated about 650 feet southeast of the Serpent effigy. The conical mound had been excavated by Putnam and was found to contain multiple burials and associated grave goods. Analysis of these materials by world-renowned expert James B. Griffin (1943:56-64) identified diagnostic Adena projectile points and pottery. Additional Adena materials were further identified by Griffin from nearby features. As Putnam anticipated, Griffin also found evidence for a much later Fort Ancient occupation of the area. The totality of evidence, however, led Griffin (1943:57) to conclude: "Although artifacts taken by Putnam from the conical mound south of the serpent and from the lower level of the near-by village site cannot be positively assigned to the builders of the effigy, it is considerably less likely that the later Fort Ancient occupants built the serpent." Both the consensus of opinion and radiocarbon evidence suggest an Adena construction.

On a final note, it is useful to consider that although Serpent Mound is an exceedingly sophisticated earthwork in terms of its design, there are are other examples of similarly complicated earthwork designs found in the Eastern Woodlands that predate Serpent Mound - in some cases by thousands of years. Watson Brake and Poverty Point are examples. Watson Brake is solstice-aligned (Davis 2012; Romain 2013) and designed using geometric shapes (Sassaman and Heckenberger 2004). So too, Poverty Point is one of the most impressive earthworks ever built and like Watson Brake, uses geometric shapes in its design (Clark 2004; Romain and Davis 2013). Watson Brake dates to about 3400 B.C. (Saunders, et al. 2005:1); Poverty Point dates to about 1600 B.C. (Gibson 2001:94). Given this, there is no reason to think that intricate earthwork designs such as found in the Serpent Mound were beyond the capabilities of Adena people at ca. 321 B.C. The imaginations of Adena people were most certainly not limited to building circle earthworks and conical mounds. Indeed, if archaeologists have learned anything over the past decades it is to not underestimate the capabilities and accomplishments of the ancient cultures and people we endeavor to understand.


I wish to express my sincere thanks to the principal investigators who made-up the core of the Serpent Mound team: G. William Monaghan, Edward W. Herrmann, Timothy M. Schilling, Jarrod Burks, Karen Leone, Alan Tonetti, Matthew Purtill, and Michael J. Zaleha. All volunteered their time and expertise. Each played a crucial role; each was a delight to work with.

Many other persons contributed
time, effort, and material support to The Project including: Jeff Wilson, Delsey Wilson, Albert Pecora, Jim McKenzie, Beverly McKenzie, Ross Hamilton,
Lesley LaBoda, Kris Phipps, Glen Horton, Jeff Dilyard, Harry Campbell, Jamie Davis, Dave Kuehner, Crystal Marvin, Meggan McCane, and Horton Hobbs. Thank you.

Permission to conduct research at Serpent Mound was granted by the Ohio Historical Society. For various OHS assistance and support we thank Burt Logan, George Kane, Brad Lepper, Bill Pickard, and Karen Hassel.

GeoProbe equipment was graciously provided by the Glenn A. Black Laboratory of Archaeology. Funding for radiocarbon dating was very generously provided by Friends of Serpent Mound, Gray & Pape, Inc., Ohio Valley Archaeology, Inc., and ASC Group, Inc.

Thank you to all.

William F. Romain, Ph.D.
Director, The Serpent Mound Project


Bronk Ramsey, C.
2013  OxCal 4.1 Manual. Electronic document, html, accessed November 2013.

Clark, John E.
2004  Surrounding the Sacred: Geometry and Design of Early Mound Groups as Meaning and Function. In Signs of Power: The Rise of Cultural Complexity in the Southeast, edited by Jon L. Gibson and Phillip J. Carr, pp. 214-233. University of Alabama Press, Tuscaloosa.

Davis, Norman L.
2012  Solar Alignments at the Watson Brake Site.
Louisiana Archaeology 34:97-115.

Fletcher, Robert V., Terry L. Cameron, Bradley T. Lepper, Dee Anne Wymer, and William Pickard.
1996  Serpent Mound: A Fort Ancient Icon? Midcontinental Journal of Archaeology 21 (1):105-43.

Greenman, Emerson F.
1934  Guide to Serpent Mound (booklet). Ohio Historical Society, Columbus.

Gibson, Jon L.
2001  The Ancient Mounds of Poverty Point: Place of Rings.
University Press of Florida, Gainesville.

Griffin, James B.
1943  The Fort Ancient Aspect: Its Cultural and Chronological Position in Mississippi Valley Archaeology, Anthropological Papers No. 28, Museum of Anthropology, University of Michigan, Ann Arbor.

Herrmann, Edward W., G. William Monaghan, William F. Romain, Timothy M. Schilling, Jarrod Burks, Karen L. Leone, Matthew P. Purtill, and Alan C. Tonettti
2015  Radiocarbon Dating of Serpent Mound. In Serpent Mound Revealed: Context, Archaeology, and Meaning, edited by William F. Romain. Book manuscript in preparation.

Herrmann, Edward W., G. William Monaghan, William F. Romain, Timothy M. Schilling, Jarrod Burks, Karen L. Leone, Matthew P. Purtill, and Alan C. Tonetti
2014  A New Multistage Construction Chronology for the Great Serpent Mound, USA. Journal of Archaeological Science 50:117-125. Electronic document,, accessed July 2014.

Putnam, Frederic W.
1890. The Serpent Mound of Ohio. Century Illustrated Magazine 39:871-888.

Reimer, P. J., E. Bard, A. Bayliss, J. W. Beck, P. G. Blackwell, C. Bronk Ramsey, P. M. Grootes, T. P. Guilderson, H. Haflidason, I. Hajdas, C. Hatte, T. J. Heaton, D. L. Hoffmann, A. G. Hogg, K. A. Hughen, K. F. Kaiser, B. Kromer, S. W. Manning, M. Niu, R. W. Reimer,  D. A. Richards, E. M. Scott, J. R. Southon, R. A. Staff, C. S. M. Turney, and J. van der Plicht
2013  IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0-50,000 years cal BP. Radiocarbon 55(4):1869-1887.

Romain, William F.
2013  Letter to the Editor Regarding Watson Brake. Louisiana Archaeology 36 (2009, printed February 2013):3-4.

1987  The Serpent Mound Map. Ohio Archaeologist 37(4):38-42.

Romain, William F. and Norman L. Davis
2013  Astronomy and Geometry at Poverty Point. Louisiana Archaeology. Electronic document,, accessed July 2014.

Sassaman, Kenneth E., and Michael J. Heckenberger
2004  Crossing the Symbolic Rubicon in the Southeast. In Signs of Power: The Rise of Cultural Complexity in the Southeast, edited by J. Gibson and P. Carr, pp. 214-233. University of Alabama Press, Tuscaloosa.

Saunders, Joe W., Rolfe D. Mandel, C. Garth Sampson, Charles M. Allen, E. Thurman Allen, Daniel A. Bush, James K. Feathers, Kristen J. Germillion, C. T. Hallmark, H. Edwin Jackson, Jay K. Johnson, Reca Jones, Roger T. Saucier, Gary L. Stringer, and Malcolm F. Vidrine
2005  Watson Brake, A Middle Archaic Mound Complex in Northeast Louisiana. American Antiquity 70(4):631-668.

Webb, William S., and Raymond A. Baby
1957  The Adena People No. 2. Ohio Historical Society, Columbus.

Webb, William S., and Charles E. Snow
1945  The Adena People. Reports in Anthropology and Archaeology, Vol. VI. University of Kentucky, Lexington.

Above: Map of Hopewell Mound Group (Shetrone 1926:196) superimposed over LiDAR image showing location of Great Circle Woodhenge.

Recent discoveries suggest that an Adena or Hopewell woodhenge - perhaps dating to around 2,000 years ago, was designed using sophisticated geometric concepts, built to a special size, and aligned to the summer solstice. 

The newly-discovered woodhenge is located within an earthen walled enclosure known as the Hopewell Mound Group. Situated in Ross County, Ohio, the Hopewell Mound Group is the namesake for the Hopewell Culture and is one of the largest Hopewell sites known. Before it was plowed-down by farming and dug into for its buried grave goods, the site included at least 40 mounds and more than three miles of embankment walls.
Today, the site is protected by the National Park Service and is part of the Hopewell Culture National Historical Park.

The Great Circle embankment shown on the Shetrone map (above) and Squier and Davis map (below) is one of the features that was severely plowed. Today, the embankment is not visible to the naked-eye, or in LiDAR imagery. Originally, however, the more complete Great Circle feature consisted of the earthen embankment shown on the early maps, plus the newly discovered circle of wooden posts (i.e., the woodhenge), as well as an exterior ditch.

Remnants of the Great Circle ditch and woodhenge were first detected during a limited  magnetic gradiometer survey by archaeologist Jennifer Pederson Weinberger (2006). Subsequent to that, a large-scale gradiometer survey showing the entire ditch and woodhenge area was completed by archaeologist Jarrod Burks (2014, 2013) pursuant to contract with the National Park Service. It is the Burks mag imagery that is shown here.

The woodhenge is comprised of a series
of large post holes (estimated by Burks [2013:30] to originally number about 108 for the presumed complete post circle), surrounded by a ditch, 6.5 - 8.2 feet wide (2.0 - 2.5 m). It is the ditch feature that shows-up so prominently in the magnetic gradiometry imagery as a dark circle.
It is not entirely clear at this point if the embankment wall shown on the early maps was exterior to the woodhenge, or if it was built over the post holes after the posts were removed. That is one of the questions currently being investigated by National Park Service archaeologists under the direction of NPS archaeologist Bret Ruby (2014b).
Above: Squier and Davis (1848:Pl. X) map of the Hopewell Mound Group.
Above: magnetic gradiometer image with alignment, geometry, and mensuration data added.
Above: although at map scale the Great Circle looks small; it is actually quite enormous. This photo was taken from the approximate center of the Great Circle. The archaeology crew is seen in the distance, excavating at the exterior ditch. Photo by Romain.
Above: NPS excavation crew, clockwise from lower left: Patrick Zingerella, Jocelyn Connolly, Bret Ruby, Andrew Weiland, Nissa Salvan, Jarrod Trombley. Cailey Mullins is in the center. Not pictured: Timothy Everhart. Photo credit: Tim Black and Dean Alexander, provided courtesy of Bret Ruby.
Above: Photo showing profile of exterior ditch.
Below: Photo showing profile of excavated post hole. Photos by Romain.


William F. Romain, Ph.D.

The Adena and Hopewell aligned many of their earthworks to celestial events such as solstices. They also built many earthworks in geometric shapes and used standard units of measurement (Hively and Horn 1982; Romain 2000). One of these units of measurement is equal to 1,054 feet. For convenience, we can call this the Hopewell Measurement Unit, or HMU. Thus 1 HMU = 1,054 feet. This unit of length is based on the diameter of the Newark Observatory Circle (Thomas 1894:16). This unit of length or its sub-multiples (e.g., 527 ft., 263.5 ft., 131.7 ft.) are found in the dimensions of every Hopewell earthwork assessed thus far, as well as most Adena earthworks.

1/4 HMU = 263.5 feet

If a square having sides that are each 1/4 HMU (or 263.5 ft.) in length is constructed, then the resulting diagonal will be 372.6 feet.

According to Burks (2013:30) the diameter of the inside edge of the Great Circle ditch is 114 meters, or 374 feet.
Accordingly, the inside diameter of the Great Circle is equal to the ideal 1/4 HMU square hypotenuse length to within 1.4 feet (negligible at ground level and at map scale). It is not uncommon to find Adena and Hopewell earthworks sized using similar iterations of the HMU based on hypotenuse lengths.

The interesting thing about the Great Circle design is that the summer solstice alignment is orthogonal to the diagonal of the 1/4 HMU square; and further, the diagonal of the square and its solstice orthogonal establish the locations for at least two of the gateways into the circle. In this design, astronomic observations, geometry, and a specific unit of length are integrated in a sophisticated and unique way.

The interior post holes that comprise the woodhenge are of special interest. As mentioned, it is estimated that there may have been about 108 post holes. A likely reason why all of the posited post holes are not visible in the mag imagery is explained by Burks (2013:30):
"Not all of the posts are visible in the magnetic data and this could be because those postholes that were detected contain burned earth, while others do not."

Excavation into two post hole features by Bret Ruby (2014a) and colleagues revealed that the post holes are about 4 feet deep. The posts that were set into these holes were roughly 2 1/2 feet in diameter. Ruby (2014a) calculates that four-foot deep holes
could have supported poles as tall as 18 feet. Note too the four pit-like features at the center of the circle. These may be additional post holes or other kinds of features.

For more details concerning excavation of the post holes, see the NPS video:

There are several things worth noting about the discoveries just documented.

First, this is the only Adena-Hopewell woodhenge I know of that is not only solstice-aligned, but also uses the orthogonal of that alignment to establish a second opening into the circle. The significance of this finding is that it demonstrates in a ground-truthed manner, the importance of orthogonal relationships relative to astronomic sightlines - a design variable that was used at other sites to include those of the later Mississippian period.

Second, this work demonstrates that much remains to be discovered about the ancient Adena and Hopewell. All is not lost. Although seemingly plowed into oblivion, new technologies can - in some cases, retrieve useful data. We must continue to support and fund the kind of research demonstrated by this project.

Lastly, studies such as this demonstrate the value of using multiple approaches in our efforts to understand the past. In this case, geophysics combined with excavation, combined with archaeoastronomic assessment yielded informative results - thereby furthering our understanding....And that after all, is the point of what we do as archaeologists.


I wish to thank Jarrod Burks, Ph.D., and Bret Ruby, Ph.D. for sharing their discoveries of the Great Circle woodhenge with me and for various permissions. Many thanks also to the National Park Service archaeology crew for showing me their excavations.


Burks, Jarrod
2014  Recent Large-Area Magnetic Gradient Surveys at Ohio Hopewell Earthwork Sites. International Society for Archaeological Prospection ISAP News 39:11-13.

2013 Large Area Magnetic Survey at the Hopewell Mound Group Unit, Hopewell Culture
National Historical Park, Ross County, Ohio, OVAI Contract Report #2012-52-1. Contract
P12PX15855. Prepared for Midwest Archeological Center, National Park Service, Lincoln, NE.
Prepared by Ohio Valley Archaeology, Inc., Columbus, Ohio.

Hively, Ray, and Robert Horn
1982 Geometry and Astronomy in Prehistoric Ohio. Archaeoastronomy
(Supplement to Vol. 13, Journal for the History of Astronomy) 4:S1-S20.

Pederson Weinberger, Jennifer
2006 Ohio Hopewell Earthworks: An Examination of Site Use from Non-Mound Space at the Hopewell Site. Unpublished Ph.D. dissertation, Department of Anthropology, The Ohio State University, Columbus, Ohio.

Romain, William F.
2000 Mysteries of the Hopewell: Astronomers, Geometers, and Magicians of the Eastern Woodlands. University of Akron Press, Akron, Ohio.

, Bret J.
2014a Current Research in the Park: The Great Circle Project at Hopewell Mound Group. Presentation for the National Park Service Harness Lecture Series, June 26, 2014, Hopewell Culture National Park, Chillicothe, Ohio.

2014b Research Design to Evaluate the “Great Circle” at Hopewell Mound Group. Report on file, National Park Service, Hopewell Cultural National Historical Park, Chillicothe, Ohio.

Shetrone, Henry C.
1926 Explorations of the Hopewell Group of Prehistoric Earthworks. Ohio Archaeological and Historical Quarterly 35:5-227.

Squier, Ephraim G., and Edwin H. Davis
1848 Ancient Monuments of the Mississippi Valley; Comprising the Results of Extensive Original Surveys and Explorations. Smithsonian Contributions to Knowledge, Vol. 1. Smithsonian Institution, Washington, D.C.

Thomas, Cyrus
1894 Report on the Mound Explorations of the Bureau of Ethnology for the Years 1890-1891. In Twelfth Annual Report of the Bureau of American Ethnology. Smithsonian Institution, Washington, D.C.

Chief Crowfoot (1830 - 1890), warrior and chief of the Siksika FIrst Nation.

As Chief Crowfoot lay on his deathbed, his last words reportedly went something like this:

"A little while and I will be gone from among you. Whither I cannot tell.
From Nowhere we came; into Nowhere we go.

What is life? It is the flash of a firefly in the night.
It is the breath of a buffalo in the winter time.
It is as the little shadow that runs across the grass and loses itself in the sunset."

In future blogs I will open conversations about earthwork preservation and related matters. For this first posting, however, I
wish to advocate for a particular way of being-in-the-world.

Chief Crowfoot's last words are profound and hold deep meaning. They remind us that our time is brief; and they give us pause to think about our place in the scheme of things. 

Reflecting on these matters, is it not true that all life is interconnected and interdependent? And, is it not true that all life forms have inherent value and worth?

If these statements are true, then it seems to me that, as human beings, we
have an affirmative obligation to make the world a better place during our brief stay. This obligation derives from the fact that as sentient, empathetic beings, we are among the privileged few that have the ability to see several actions into the future and based on those predicted outcomes, make moral choices for good. Moreover, we possess the physical capabilities to make those outcomes happen.

Of course how one defines 'good' differs among people; and all too often we have seen the tragic consequences of other peoples' notions about what is 'good' for the rest of us. That said, the definition I endorse basically holds that  'good' is a way of interacting with the world that increases the quality and quantity of available choices without causing harm to others.

There are many ways we can actualize good. The important thing is that we do something....

So in this first blog, I wish to advocate for action that in whatever way, big or small,  maximizes 'good' - which is to say, makes the world a better place. Become an advocate for animal rights; become an advocate for human rights; become an advocate for environmental causes; become an advocate for the preservation of our collective cultural heritage through earthworks preservation.

Whatever cause you choose; do something. For although as individuals we may be little more than a "flash of a firefly in the night", I believe that, together, we - as in seven billion people, can light-up the universe.

William F. Romain