The Great Circle was once called the “Old Fort” because people believed its interior ditch served as a moat, but a defensive moat would normally be outside rather than inside the walls. In 1839, Cornelius Matthews recognized this problem yet still argued that the Great Circle was a fort built on military principles that were lost or inexplicable. The water-filled ditch instead may have served a ceremonial purpose, perhaps as a barrier that spirits of the dead could not cross or as a symbolic version of the watery Beneath World on which the Middle World floated in many American Indian traditions.