Woodhenge is a circle of wooden posts at Cahokia Mounds Illinois. It is west of Monk's Mound which is the largest man-made earthen mound in North America The placement of the posts mark the summer and winter solstices (21 of June, 21 December) and the spring and autumn equinoxes (21 March, 22 September). In short, the posts are a calendar, similar to the stone equivalent on the British Isles. The first woodhenge to be discovered at this site was 410 feet in diameter and contained 28 posts. Later four more circles were discovered and of the five, one has 24 posts, one with 36, the first discovered with 48, another with 60 and the last one, which has only partially been uncovered but it is likely that it had 72 posts. The posts were made originally of red cedar which was considered sacred to the natives. Red ochre has also been found which suggests the possible remains of red paint on the original posts.
Woodhenge was built several times during the history of the Mississippian people and again with the Cahokia people so it must of held some important significance. The most obvious answer is that it was a calendar. It certainly is a calendar but it may have had more meaning than that. Some have suggested that the posts represented some kind of engineering device to assist in the layout of the city. Also, due to the sacred red cedar and a number of artifacts found on or near the site it may have also been used religiously.
The first of the five circles was discovered accidentally in 1961 by Dr. Warren Wittry. Near the post marking the winter solstice a beaker with a circle and a cross symbol was found. This artifact may have symbolized the earth and its four directions. The beaker also had several radiating lines which in many cultures signifies the sun. Soon after another woodhenge was found near mound 72 of the Cahokia Mounds. Evidence now suggests that there are at least five circles, each of a different size. The reconstructed Woodhenge, as shown above, was erected in 1985.