|An Illustration of the Cahokia Woodhenge.|
DISCOVERY AND EXCAVATION
The existence of the series of woodhenges at Cahokia was discovered during salvage archaeology undertaken by Dr. Warren Wittry in the early 1960s in preparation for a proposed highway interchange. Although the majority of the site contained village house features, a number of unusually shaped large post holes were also discovered. The post holes were 7 feet in length and 2 feet in width and formed sloping ramps to accommodate the insertion and raising of the estimated 20 feet tall posts to a 4 feet depth into the ground. When the holes were plotted out it was realized that they formed several arcs of equally spaced holes. Detailed analytical work supported the hypothesis that the placement of these posts was by design. Wittry hypothesized that the arcs could be whole circles and that the site was possibly a calendar for tracking solar events such as solstice and equinoxes. He began referring to the circles as "woodhenges"; comparing the structures to England's well-known circles at Woodhenge and Stonehenge.
|Woodhenge lies to the west of Monks Mound, at the lower left edge of the illustration.|
The remains of several posts were discovered in the post pits. The type of wood used, red cedar (Juniperus virginiana), is considered sacred by many Native American groups. The red cedar is the only native evergreen species in the area and is resistant to disease and decay. Traces of red ochre pigment was also found, suggesting that the posts were probably painted at some point. In 1985 William R. Iseminger led a series of excavations to finish finding a full circular sequence of posts. He was able to complete the sequence for what has become known as Woodhenge 3 (except for nine posts on the western edge that had been lost to dump trucks for road construction fill) and then led a reconstruction of the circle. The reconstruction team was able to obtain enough red cedar logs for half of the holes and then made do with black locust (Robinia pseudoacacia) for the other half; placing them into the original excavated post positions. The Illinois Historic Preservation Division (a division of the Illinois Department of Natural Resources) oversees the Cahokia site and hosts public sunrise observations at the vernal and autumnal equinoxes and the winter and summer solstices. Out of respect for Native American beliefs these events do not feature ceremonies or rituals of any kind.
The structure was rebuilt a number of times during the city center's roughly 300 year Woodhenge history. The presence of single set posthole houses and midden  deposits at the location suggests the area was a habitation area during the early Emergent Mississippian period; before the timber circles were constructed. And a separate layer of later Mississippian wall trench houses suggests it became a habitation area again after the final woodhenge was no longer in use.
Woodhenge 1 was located to the east of the other circles, the only one not built on the same spot as the other four. It had 24 posts and was 240 feet in diameter. This circle was dismantled and at a later date Mound 44 was constructed, partially covering this location.ALIGNMENTS
Woodhenge 2 was constructed to the west of the previous circle. It had 36 posts and was 408 feet in diameter.
Woodhenge 3 had 48 posts and was 410 feet in diameter. It is thought to have been constructed in approximately 1000 AD. This version of the woodhenge was reconstructed in 1985 using the original holes found during excavations. The 48 posts of the circle are set at 7° 30′ apart as measured from the geometric center of the circle, although the central post of the circle is offset from the true center by 5.6 feet to the east. This facilitates the alignment with perimeter posts marking the winter and summer solstice sunrise positions, correcting for the latitude of Cahokias location.
Woodhenge 4 had 60 posts and was 476 feet in diameter.
Woodhenge 5 had an arc and post spacing that suggests it was 446 feet in diameter and could have had 72 posts, although only 13 posts were found in a short arc facing the direction of the sunrise. Archaeologists suspect it may not have been a full timber circle and that by this time the large trees needed for the posts may have been getting scarce in the vicinity of Cahokia.
The woodhenge is thought by archaeologists to be a solar calendar, capable of marking equinox and solstice sunrises and sunsets for the timing of the agricultural cycle and religious observances. During the equinoxes the sun rises due east of the timber circle. From the vantage point of the center of the circle it appears as if the sun is emerging from the front of Monks Mound which is roughly a half mile away. One of the reasons for the changing position and size of the timber circles may have been the growing size of Monks Mound as additional layers of earth raised its height and increased its geographic footprint and the desire to keep this symbolic emergence and alignment intact.
|View of the reconstructed Woodhenge 3 and its alignment with the equinox pole. You can see Monks Mound which is 1/2 mile away.|
The winter solstice sunrise pole is aligned with the Fox Mound (Mound 60, a rectangular platform mound paired with a conical burial mound, Mound 59) which sits across the grand plaza 1,640 feet to the south of Monks Mound. The top of the roughly 46 foot tall mound projects above the horizon and in Cahokian times would have had a large temple structure at its summit, raising it even higher. From the central pole of Woodhenge 3 the sun would have appeared to rise from this mound and temple at the winter solstice. Besides their celestial marking functions, the woodhenges also carried religious and ritual meaning that are reflected in their stylized depiction as a cross in circle motif on ceremonial beakers.
|Ceramic beaker with woodhenge motif.|
As there are many more posts than are necessary for these simple alignments some archaeoastronomists have speculated that they were also used to observe other celestial events, such as lunar cycles, the motion of the Pleiades star cluster , or other stars and planets; while others have suggested they were used to align mound and causeway constructions projects.
CAHOKIA'S MOUND 72 WOODHENGE
Archaeologist Marvin Fowler has speculated that the woodhenges also served as "aligners" and that there may have been as many as three more in other strategic locations around the city of Cahokia, built to triangulate and lay out construction projects. At least one other possible circle at Cahokia has been put forward by Fowler, but his suggestion has not yet gained full acceptance by other archaeologists.
This location was discovered near Mounds 72 and 96, directly to the south of Monks Mound. Several post holes of what may have been a ceremonial area with a 412 feet in diameter circle and 48 posts. Archaeologists have dated the placement of at least one of the posts to approximately 950 AD.
|Solstice and equinox markers at the Mound "Md" 72 Woodhenge, with the hypothesized full circle of posts.|
The Birdman tablet was discovered in 1971, during excavations at the base of the eastern side of Monks Mound, conducted by the University of Wisconsin at Milwaukee.
|The Real Cahokia "Birdman Tablet."|
Also found onsite was the Ramey Tablet. The tablet was found east of Monks Mound on the Ramey farm sometime during the 19th century. It dates to around 1250 AD. The Ramey tablet is broken in quarters. Only one-half of the tablet was found. The original Ramey tablet is in the collection of the Madison County Historical Museum in Edwardsville, Illinois.
|The Ramey Tablet displays war symbols of the Southeastern Ceremonial Complex with human heads, hair buns, beaded forelocks, ear spools, and pileated woodpeckers.|
 A midden is an old dump for domestic waste which may consist of animal bone, human excrement, botanical material, shells, sherds, and other artifacts and ecofacts associated with past human occupation.
 The Pleiades star cluster – also known as the Seven Sisters or M45 – is visible from virtually every part of the globe. It can be seen from as far north as the North Pole, and farther south than the southernmost tip of South America. It looks like a tiny misty dipper of stars.
|This star chart for M45 represents the view from mid-northern latitudes for the given month and time.|
|Pleiades Star Cluster.|