A unique feature of the circle is the so-called crown work opposite the opening to the octagon. This oval mound is 170 feet long and approximately 8 feet higher than the adjoining portions of the circle. Since the mid-19th century, this mound has been called the observatory because it overlooks the rest of the circle and octagon. Recently, some researchers noticed that a line drawn from the observatory to the opposite side of the octagon points to the location on the horizon where the moon rises at its most northerly position. If the Hopewell people intended for the earthworks to be oriented toward the rising moon, then the name observatory may be especially appropriate.