I . Calcite font, Mosan, about I 200. Diameter 5I h incht someone else's research or the discovery of a new artifact or document, and a stymied investigation may be started afresh, sometimes after a lapse of decades. One of the rrsost famous cases of the missing central clue is that of the carved medieval alabaster plaques. These small reliefs, measuring about a foot by two feet and depicting t...