Moorehead Circle, 2,000 year-old concentric rings of timber posts, lies northeast of Cincinnati, Ohio (USA). It was first discovered in 2005 by ground-penetrating technology. Now archaeologists using computer models have discovered that openings in the rings, stone mounds, and a gate in an earthen wall are all aligned with the sunrise at the summer solstice. Robert Riordan, an archaeologist from Wright State University, the director of the excavation explained that the software "allows us to stitch together various kinds of geographical data, including aerial photographs and excavation plans and even digital photographs."
     The timbers that once defined the structure are gone, leaving only postholes filled with rocks. The holes are 10 inches across and up to 3 feet deep. It is believed that they held posts made from local trees, including oak and hickory. The posts may have stood 10 to 13 feet above the ground. Some holes are dug only inches apart from each other. The site is approximately 200 feet wide. Nearby is the Fort Ancient State Memorial, an earthworks built by the Hopewell culture of native peoples. They occupied the American midwest and east for almost a thousand years from 2000-1000 BPE.
     At the center of the circles is a cleared area containing burned soil heavily littered with fragments of pottery. In a 2007 excavation, Riordan and his team found trenches filled with clay and ash covered with gravel and soil. It is not known how these were used.
     Riordan notes that construction of the circles required a significant expenditure of resources. "They would have had to dig these holes, go get the trees, cut them, strip them, and carry them in," Riordan said. The limestone rock fragments found in the holes were carried froma quarry about a mile away and up a significant grade. The Hopewell peoples did not have metal tools and would have dug the postholes with sharpened bone and wood implements.
     Riordan believes that the wooden posts would have decayed within the lifespan of many of the builders, probably lasting only about 10 years. "This was an elaborate construction," he added. "All the effort that went into constructing it suggests it was the ceremonial focus of Fort Ancient for a time."

Source: National Geographic (20 June 2010)