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SEARCHING FOR THE SWEET LIFE

Excavations at Chatsworth Plantation in East Baton Rouge Parish, funded by grant from SEAC (Southeastern Archaeological Conference)


ASTRONOMY AND GEOMETRY AT POVERTY POINT

William F. Romain and Norman L. Davis

More than three thousand years ago, in northeastern Louisiana, Native Americans built an enormous earthwork complex that is unique in all the world (Figure 1). At a minimum, the complex covers 162 hectares (400 acres) (Gibson 2001:4) and includes the second largest mound north of Mexico (Kidder 2011: 97). The earthwork builders built this complex using sophisticated geometric shapes. Moreover, they aligned these shapes to celestial events. The earthwork complex is known as Poverty Point.

Figure 1. Artist's representation of Poverty Point. Drawing by Herb Roe.


Background

The notion that Poverty Point was constructed using geometric shapes is not new. Early-on the site was described as a series of concentric circles or octagons (e.g., Ford and Webb 1956:16). Based on more recent ground surveys the site is better described as a series of concentric C-shaped ridges. If the trajectory of these ridges were to be extended into the swampy area off to the east, they would form a series of nested ovals or ellipses. Likewise, the idea that the site is aligned to celestial events is not new. More than thirty years ago, Brecher and Haag (1980, 1981, 1983; also see Haag 1993) suggested that the northwest and southwest aisles that crosscut the concentric rings were oriented to the solstices. Contrary to this, Robert Purrington (1983; also see Purrington and Child 1989) argued that the aisles were not solstice-aligned. LiDAR analysis shows that Purrington was correct - the summer solstice sunset is not in alignment with the northwest aisle. And while Brecher and Haag's posited winter solstice sightline through the southwest aisle is a better fit, it is off by about 6.5 degrees, or the equivalent of 13 sun diameters. Purrington offered alternative stellar alignments; but ultimately, neither Brecher and Haag, nor Purrington's alignments were widely accepted - basically because accurate maps were not available for rigorous assessments.

Thus the situation rested for several years until newly acquired LiDAR data were utilized by the authors to re-assess potential alignments. LiDAR is an acronym for Light Detection and Ranging. The technology uses reflected near-infrared laser beams aimed at the earth from an aircraft, to develop accurate images of the ground topography (Romain and Burks 2008a, 2008b, 2008c). Figures 2 - 5 show images for Poverty Point using LiDAR data retrieved from the Louisiana Statewide GIS Atlas (http://atlas.lsu.edu/). As Figure 2 shows, the Poverty Point complex is comprised of at least five mounds (not including the Motley Mound about 2 km to the north and Lower Jackson Mound about 3 km to the south), six concentric man-made ridges with swales in-between and crosscut by two or three aisles, a central plaza, and several borrow pits.

Mound E is a flat-topped rectangular-shaped mound, about 4 meters in height. Approximately 30 meters of the southern extent of the mound has been truncated in modern times by road construction and land leveling (Diana M. Greenlee, personal communication 2013; Kidder, et. al. 2004). In Figure 2, the dotted black line shows the estimated original footprint of Mound E.

Mound B is a conical mound about 6 meters in height and 60 meters in diameter (Ortmann 2010:665). It was built in several stages (Gibson 2001:87; Kidder et. al. 2004).

Mound A is an enormous, combination platform mound, conical mound, and ramp. It is about 22 meters in height, 207 meters in width and 210 meters in length (Ortmann and Kidder 2013:67). It is one of the largest mounds in North America and appears to have been built very quickly - in a matter of months (Ortmann and Kidder 2013:66). 

Mound C is best-described as an "oval shaped conical mound" (Ortmann 2010:668). Today it is about 60 meters in length. Its original width is uncertain, as it has been eroded by the Bayou Macon. At present the mound is about 2.6 meters in height, with about 2 meters of the mound above the present plaza surface and 0.5 - 0.6 meters below the surface (Diana M. Greenlee, personal communication 2013). Mound C is comprised of at least 16 thin layers of prepared surfaces of different colored and textured soils at its base, capped by a 1.5-meter layer forming the conical shape of the mound. Post holes suggested to Gibson (2001:88) that "post-in-ground" structures were built on several of the floors. Artifact evidence including hematite, red ochre, crystalline quartz, and other materials led Gibson (2001:89) to further conclude that Mound C activities were of a "sacred and ceremonial character." Related are Ortmann's (2010:669) comments that: "The Mound C stratigraphy indicates it was not a mound during its initial construction history. The series of prepared floors were purposeful constructions that did not appreciably raise the height of the feature."  Further, "Although it may not have been distinguishable from the plaza as a raised architectural feature, the unique construction methods and unique signature of cultural debris and features suggest it was differentiated from the rest of the site as a specialized activity area" (Ortmann 2010:669).

As to its age, Ortmann and Kidder (2013:75) find that: “Mound C, or at least part of it, was built and used while the ridges were being constructed” (also see Ortmann 2010:672). Both Gibson and Ortmann's conclusions about the special nature of the mound, and Ortmann and Kidder's findings about the age of the mound are important points – for as discussed later, Mound C was an ideal location from which to observe the solstices during the Poverty Point occupation. Indeed, the discovery of specially prepared ground-level floors that ostensibly marked the backsight location for such observations is consistent with this suggested use.

Mound D is a small rectangular mound, about 2 meters in height. Radiocarbon-dated charcoal from deep within the feature and diagnostic artifacts date to Poverty Point times (Ortmann 2010:667-668). OSL dates and ceramics from higher levels, however, indicate that significant mound construction occurred during the time of the Coles Creek culture (ca. A.D. 700 - A.D. 1200) (Greenlee 2011) - long after the Poverty Point florescence. Mound D is located on the elliptic trajectory of Ridge 2. The ridge itself, however, at least in the southeast area of the site, has been severely impacted by modern topographic changes. As a result, it is not possible to visually determine whether Ridge 2 extended as far east as Mound D. As a consequence, opinions have been divided on whether Mound D is a Coles Creek mound built on top of a Poverty Point ridge; or alternatively, is it a discrete Poverty Point mound that was built-up by the later Coles Creek culture and not part of the ridge system? The most recent data and opinion support the idea that Mound D was built on top of Ridge 2 (Greenlee 2011; Ortmann 2010:667). If that is the case then due to its location on the bluff edge, Mound D likely marked the southeast terminus for Ridge 2. If Mound D started-out as a discrete Poverty Point mound, then its location at the edge of Bayou Maçon is an interesting choice, perhaps related to the extensive view to the east from that location. Either way, Mound D apparently held special significance - including its role in a solstice alignment, discussed below.

As to the rings, or ridges, the northern ridges are relatively undisturbed and between 1 – 2 meters in height. The southern ridges are lower - i.e., 20 - 30 cm in height and have been subjected to plowing, although they may not have been as topographically distinct as the northern ridges to begin with (Diana M. Greenlee, personal communication 2013).  The ridges are separated by depressions or swales. Ridge 1 is labeled in Figure 2 and was central to the overall design of the complex.

Figure 2. LiDAR image of Poverty Point showing Ridge 1 and mound locations.


Temporal sequencing of mound construction at Poverty Point is the subject of continuing research. Gibson (2001:96) suggests that most mound and ridge construction took place between about cal. 1600 B.C. to 1300 B.C. (but see Connolly 2006; Ortmann 2010; and Ortmann and Kidder 2013, who suggest a wider time span). Whatever the exact sequence and time span of mound building, there seems little doubt that there was a "massive building boom at Poverty Point" that ended with the very rapid construction of Mound A at ca. 3400 to 3200 cal. yr. B.P. (Ortmann and Kidder 2013:75). Of course this does not really address the question as to whether or not the end product that we see on the ground today is the result of a master design plan envisioned by the founders of Poverty Point; or, is the final form the result of a "self-organizing phenomenon" that presents the illusion of a planned design "because its parts articulate so well" (Kidder 2011:117)? The question is not unique to Poverty Point. Indeed, almost every large-scale prehistoric manifestation - whether Poverty Point, Cahokia, the Newark Earthworks Complex, or Chaco Canyon is subject to the same question.

Ortmann and Kidder (2013:78) propose that: “The complexity of the construction process at Poverty Point demonstrates the venture was well planned and organized, and was undertaken to transform the landscape into a preconceived and desired form.” To this we would add that, based on the seamless integration of site orientation, celestial alignments, bilateral symmetry of design points, internal geometry, regularities in mensuration and relatively rapid monument building, we believe construction likely proceeded - at least for the most part, pursuant to a master plan or design template. The caveat is that such a plan did not necessarily need to include every mound and ridge - as long as additional constructions incorporated basic design principles understood by successive mound builders and were consistent with the basic master design. The end results would appear the same. In either case, the following observations support the notion that Poverty Point was built according to a preconceived master plan, or again, at the very least, a series of design phases that integrated astronomical alignments, geometric shapes, and local topography.

Celestial North

The celestial north pole is the point in the heavens around which the stars and constellations appear to rotate. For many cultures, celestial north is a center place, both geographically and cosmologically. Accordingly, many cultures seek to anchor or link their monumental architecture to this center point. One way this is done is by orienting a site to true north. This works because, if an imaginary line is drawn straight down from the celestial north pole, the resulting direction on the ground will be true north. Since true north is a geographic expression of celestial north, sites that are oriented to north are by definition, astronomically aligned. (The same thing applies if the sun's meridian transit is used to determine north.) With reference to Figure 3, several observations suggest that Poverty Point was intentionally oriented to true north:

1) The sightline between mounds E-A-B (and the Lower Jackson Mound not shown here) extends north-south (Gibson 1987).

2) Ridge 1 follows the shape of an ellipse, or oval. The major axis of this ellipse is aligned north-south and is therefore parallel to the sightline between mounds E-A-B. Thus the north-south axis for the site is expressed in two different, but mutually supportive ways.

3) Mound C is situated on the north-south major axis of the inner oval.

Figure 3. LiDAR image showing Poverty Point design features and relationships.

Design Points 1 and 2


Two locations appear to have been of special importance in the design of Poverty Point. For convenience we refer to these locations as Design Point 1 (DP1) and Design Point 2 (DP2). DP1 is situated on the east side of Bayou Maçon; DP2 is situated on Ridge 1, directly opposite DP1. Both DP1 and DP2 are located where the minor axis of the Ridge 1 ellipse intersects with the perimeter of that same shape.

While DP2 is at a location that could have served as a ground-based observation point as well as a design point on a master plan, the situation is not so clear with regard to DP1. The uncertainty derives from the fact that the Poverty Point site is situated on the edge of an elevated topographic feature known as Macon Ridge. DP1 is located east of this ridge, in the Mississippi River floodplain, at an elevation about 20 feet lower than the main site. As a result, in order to see the sunsets over mounds E and B from DP1, DP1 would had to have been either a 20-foot high mound, or a built-up wooden platform.

Further complicating the matter is that although DP1 is, today, situated in a wooded swamp, Gibson (2001:7) suggests that at some point in the past, water levels in that area were higher than they are today. If he is correct, the implication is that DP1 was under water. Of course timing is everything; and even if water levels were higher in the past, what we do not know is when that might have been the case.

For the moment, however, let us assume that DP1 was under water when Poverty Point was built. Given that scenario, it may be that, rather than being an observation point, DP1 was a focal point for design purposes. In other words, if Poverty Point was built according to a scaled master plan drawn on a flat surface, using predetermined solstice azimuths, then, DP1 was simply a design point used to establish geometric and astronomic relationships between mounds. In this case, the elevation of DP1 was a moot issue since the point was simply one component of a design plan superimposed onto the landscape. For whatever reasons, the main Poverty Point site was required to be open to the east and situated on the edge of the Maçon Ridge. The result was that DP1 was going to be located off to the east - in swamp or water, no matter what. That said, the following observations support the notion that DP1 was a design focal point:

1) DP1 is situated where the east-west axis and perimeter of the Ridge 1 ellipse intersect.

2) The major axis of Mound A points to DP1.

3) The trajectory of two aisles visible in the LiDAR imagery converge at DP1.

4) The sightline from Mound B through Mound C points to DP1.

An east-west line drawn from a point halfway between the southern edge of Mound B and the northern edge of Mound E intersects the Ridge 1 ellipse at DP1. In Figure 3, the edges of mounds B and E used to establish the halfway point are shown by dotted lines.

Sunset Alignments

The following solstice azimuths (Figure 4) are calculated for 1700 B.C., (although observation dates +/- 500 years will not result in azimuth differences discernable to the naked eye), using an estimated western horizon elevation of 0°.75 degrees, corrected for refraction and lower limb tangency (where the bottom edge of the sun is tangent to the horizon). Since the horizon elevation for Poverty Point thousands of years ago is unknown and depends on tree height and the extent of area clearing, the following azimuths are likely accurate to plus or minus one degree.

1) Line DP1 to Mound B is aligned to the summer solstice sunset.

2) Line DP1 to Mound E is aligned to the winter solstice sunset.

3) Viewed from Mound C, the summer solstice sun will set over Mound B.

4) Viewed from Mound C, the winter solstice sun will appear to set not over, but rather, into the side of Mound A. The placement of Mound C near Bayou Maçon allowed for a long sightline to Mound A, but also resulted in the location for Mound A in a place that seems not-symmetrical with the overall site plan.

5) A line from DP1 through the central plaza of the site marks the azimuth of the equinox sunset along the northern edge of Mound A. One of the authors (Norman Davis) has witnessed this phenomenon from the central plaza of Poverty Point on several occasions. On these occasions the sun appeared to roll down along the northern edge of Mound A before sinking into the western horizon.

Given the redundancy of the posited alignments, observations from DP1 were not necessary if one wanted to observe these celestial events as linked to the earthworks. Indeed, as a practical matter and given the location of DP1 off in the swamp, Mound C may well have been the preferred location for actual observations.

Figure 4. LiDAR image showing posited sunset alignments. SSS = summer solstice set; WSS = winter solstice set.


Solstice Triangle

In addition to the alignments just noted, a near-perfect equilateral solstice triangle is formed by Mound B - DP1 - Mound E, and a second such triangle extends between Mound C - Mound B - Mound A (south edge). The same kind of triangle (albeit to different sizes) is found at several other Archaic sites in the Southeast (Clark 2004; Sassaman and Heckenberger 2004; Sassaman 2005) and is sometimes referred to as a Clark-Sassaman-Heckenberger Triangle. An equilateral triangle has three internal angles each equal to 60 degrees. A solstice triangle has two sides that are congruent with solstice azimuths when one side is oriented due north (Davis 2012). As shown, these conditions are met for the Poverty Point Clark-Sassaman-Heckenberger triangle to within 2 degrees of arc. Thus in addition to ellipses at Poverty Point, design triangles are in evidence.

As a center place, Poverty Point was also place of balance in the sense that, in addition to the sunset alignments just presented, conceptually opposite, sunrise alignments are also found. These alignments, shown in Figure 5, are again calculated for 1700 B.C., but this time using an estimated eastern horizon elevation of 0°.1 degree, corrected for refraction and lower limb tangency. As was the case for sunset alignments, azimuths are likely accurate to plus or minus one degree due to uncertainties in tree height and clearing.

1) Viewed from DP2, the summer solstice sun will rise over Mound C.

2) Viewed from DP2, the winter solstice sun will rise over Mound D. (If in fact Mound D was constructed more than two thousand years after the Poverty Point florescence, then, the implication is that people of the Coles Creek culture understood, incorporated, and further expanded upon the Poverty Point design for their own purposes.)

3) Viewed from DP2, the equinox sun will rise in alignment with DP1.

Admittedly one could raise various objections to the above – especially since neither DP1 nor DP2 have known marker features on the ground. On the other hand, DP1 and DP2 could have been marked by poles that have yet to be identified by postmolds. Or again, posited alignments may have simply been design components for the overall layout of the site - not all of which would necessarily be marked for viewing.

Figure 5. LiDAR image showing sunrise alignments. SSR = summer solstice rise; WSR = winter solstice rise.


Conclusion

There are many more interesting observations that could be added to this discussion. There are, for example, additional findings relevant to the geometry and mensuration of the site that have not been discussed. For now, however, the foregoing introduces what we believe to be the basic astronomical alignments and geometry of the site.

We cannot close without noting that Brecher and Haag (1980) were right in their assessment more than thirty years ago - i.e., Poverty Point does incorporate solstice alignments. Brecher and Haag's proposed alignments are not the same as what has been posited here. Nevertheless, as they suggested, Poverty Point may indeed be the world's largest solstice marker.

Of course the question that begs to be answered is: Why? Why was Poverty Point designed in such a way that it connects geometric earthen forms to celestial bodies and events at such a massive scale? Most likely there are multiple answers to this question. And certainly we claim no direct connection between the builders of Poverty Point and the Osage Indians. But there is an interesting narrative given by an Osage elder to Francis La Flesche (1930:577) that might give a clue:

The ancient No-ho-zhi-ga when formulating the tribal rites persistently held up before the people the fundamental principle that in all their activities as an organized body, a tribe, they musthave a unity of purpose and a unity of action.

They gave iterative emphasis to this fundamental principle for the reason that during their long years of contemplation of the great cosmic bodies that move through the heavens in orderly precision they had discerned the strength and power of this principle.

Perhaps by linking their great earthwork to the heavens the builders of Poverty Point sought integrate the strength, power, and order they witnessed in the heavens with their own earthly existence. Perhaps in this they found meaning and purpose.

Acknowledgements

The authors wish to thank Chip McGimsey, Dennis L. Jones, Diana M. Greenlee, and Kenneth E. Sassaman for useful comments on earlier versions of this paper. The authors are solely responsible for the content of this paper.

References Cited

Brecher, Kenneth, and William G. Haag

1980 The Poverty Point Octagon: World's Largest Prehistoric Solstice Marker?

Bulletin of the American Astronomical Society 12(4):886-887. (Abstract reprinted in 1981 in Archaeoastronomy IV(1):3.)

1983 Astronomical Alignments at Poverty Point. American Antiquity 48(1):161-163.


Clark, John E.

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Connolly, Robert P.

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