The Great Circle was built using different colored soils. In 1992, archaeologists excavated a trench through the Great Circle and discovered that the outer portion of the wall was built with dark brown soil, while the inner portion was built with brightly colored yellow-brown soil. These colors must have had a powerful symbolic meaning to the builders, but whether they kept the walls clear of vegetation so the colors could be seen, or allowed vegetation to grow over the walls, is unknown.