This new examination of an old map sheds some light on what might have happened to them. Underneath an inconspicuous patch on the map there was a drawing of a fortification. Why the patch was put on the map covering the drawing of the fort is unknown. It was common to put patches on maps when there was new information, as a quick and cheap way of updating the map without having to re-draw it completely. It was less common to put a patch over a map to obscure or obliterate some piece of information.