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).


ASTRONOMIC ASSESSMENT

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.

CONCLUDING THOUGHTS
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.

Notes
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.

Acknowledgments
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
data.

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.

References
Archaeological Conservancy
2014 Telfer Mounds (Wisconsin). Electronic document, http://www.archaeologicalconservancy.org/acquisition/telfer-mounds-wisconsin/, 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.