The History of Cahokia's Five Woodhenges.

The Cahokia Woodhenge was a series of large timbers forming a circle located roughly one-half mile west of Monks Mound in the Indian Village of Cahokia site (Collinsville, Illinois, today).

An Illustration of the Cahokia Woodhenge.

They are thought to have been constructed between 900 and 1100 AD, each being larger and having more posts than its predecessor. The site was discovered as part of salvage archaeology in the early 1960s interstate highway construction boom, and one of the circles was reconstructed in the 1980s. The circle has been used to investigate archaeoastronomy at Cahokia Mounds. Annual equinox and solstice sunrise observation events are held at the site.

DISCOVERY AND EXCAVATION
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 most of the site contained village house features, several unusually shaped large post holes were also discovered. The post holes were 7 feet in length and 2 feet in width, and sloping ramps were formed to accommodate the insertion and raising of the estimated 20-foot tall posts to a 4-foot 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 west of Monks Mound, at the lower-left edge of the illustration.

Dr. Robert L. Hall undertook additional excavations at the site in 1963. Hall used the predicted locations from the arcs found in the previous excavation and found more post holes and posts near the centers of the circles now thought to be central observation points. Wittry undertook another series of excavations at the site in the late 1970s and confirmed the existence of five separate timber circles in the vicinity. The circles are now designated "Woodhenges 1 through 5." Each was a different diameter and had a different number of posts. Because four of the circles overlap, it's thought they were built in a sequence, with each iteration generally becoming more extreme and containing twelve more posts than its predecessor.

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 were also found, suggesting that the posts were probably painted at some point. In 1985, William R. Iseminger led a series of excavations to see an entire circular sequence of posts. He completed 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 the circle reconstruction. The reconstruction team obtained enough red cedar logs for half of the holes. Then, it made do with black locust (Robinia pseudoacacia) for the other half, placing them into the originally excavated postpositions. The Illinois Historic Preservation Division (Illinois Department of Natural Resources) oversees the Cahokia site. It 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.

CONSTRUCTION SEQUENCE
The structure was rebuilt several times during the city center's roughly 300-year Woodhenge history. The presence of single-set posthole houses and midden [1] deposits suggests the area was habitation during the early Emergent Mississippian period before the timber circles were constructed. A separate layer of later Mississippian wall trench houses suggests it became a habitation area again after the final woodhenge was no longer used.

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.

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.

ALIGNMENTS
Archaeologists think the woodhenge is 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 circle's center, it appears as if the sun is emerging from the front of Monks Mound, 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 the 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 south of Monks Mound. The top of the roughly 46-foot tall mound projects above the horizon, and back in Cahokian times, it 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 reflected in their stylized depiction as a cross-in-circle motif on ceremonial beakers.

Ceramic beaker with woodhenge motif.

One prominent example has markers added to the winter sunrise and sunset positions and was found in an offertory pit near the winter solstice post pit. It also had radiating lines that symbolized the rays of the sun.

As there are many more posts than are necessary for these simple alignments, some archaeoastronomers have speculated that they were also used to observe other celestial events, such as lunar cycles, the motion of the Pleiades star cluster [2], or other stars and planets;. In contrast, others have suggested they were used to align mound and causeway construction 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 Cahokia, built to triangulate and layout construction projects. Fowler has put forward at least one other possible circle at Cahokia, but his suggestion has not yet gained full acceptance from other archaeologists.

This location was discovered near Mounds 72 and 96, directly south of Monks Mound. Several post holes may have been a ceremonial area with 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.

Archaeological research has shown that four posts were at the cardinal locations of north, south, east, and west, with eastern and western posts marking the equinox sunrise and sunset positions. Four other posts in the circle were shown to be at the summer solstice sunrise and sunset and the winter solstice sunrise and sunset positions. This setup is nearly identical to the diameter and post positions of Woodhenge 3, differing only in that Woodhenge 3 was 2 feet smaller in diameter. The placement of the two mounds at the location and the directions they are oriented correspond to several of the solstice marking posts. The post nearest the later elite burial spot of the "Birdman" is the location that marked the summer solstice sunrise at the time of the site's use. The early stages of the mounds were actually constructed around the posts, although at a later point, the posts were removed.

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."

Archaeologists theorize that the bird of prey on the front of the tablet symbolically represents the Upper World. The Middle World (of man) is represented by the human figure wearing the costume, and the Lower World is defined by the snakeskin pattern on the back of the tablet.

The Ramey Tablet was also found on site. 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 Madison County Historical Museum collection 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.

Compiled by Dr. Neil Gale, Ph.D. 

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[1] A midden is an old dump for domestic waste, consisting of animal bone, human excrement, botanical material, shells, sherds, and other artifacts and ecofacts associated with past human occupation.

[2] 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.