[3] The existence of the series of woodhenges at Cahokia was discovered during salvage archaeology undertaken by 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.

Wittry undertook another series of excavations at the site in the late 1970s and confirmed the existence of five separate timber circles in the general vicinity.

He was able to complete the sequence for what has become known as Woodhenge III (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.

[9] 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.

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 .5 miles (0.80 km) away.

[12] The top of the roughly 46 feet (14 m) tall mound projects above the horizon and in Cahokian times would have had a large temple structure at its summit, raising it even higher.

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.