The plaque commemorates the laying of the cornerstone and the dedication of the cathedral of Bayeux.  It says:
"William Duke of Normandy" is William the Conqueror who, 11 years prior, became the most recent person to successfully invade England.  (That's right... no one has done it since.)
Bishop Odon was William's brother, and the person who commissioned the creation of the Bayeux Tapestry (which we went to see even before checking into the hotel).
This, like most of France's great cathedrals, is a "working church".  Somebody goes to mass here every Sunday, and they've been doing it for 924 years.  Back then, candles gave light, witches were burned alive, the French language was what we now call "Old French"...  not what you saw on the dedication scroll...  and Latin was the lingua franca;  people came in two varieties: peasants and nobles;  there were only 4 elements: earth, air, fire, and water;  heavier weights fell faster than lighter ones;  the earth was flat and you could sail off the edge;  the authority of the King came straight from God;  plague, diphtheria, tetanus, typhus, typhoid fever, tuberculosis, measles, mumps, chickenpox, smallpox, pleurisy, and phlebitis were all fatal, arising as they did from magic and evil spirits;  almost no one died from cancer or heart disease -- they didn't live long enough;  traveling to the next town was a risky venture, traveling to another country was a death-defying feat, and nearly everyone was born, grew up, and died without ever stepping foot outside a 25-mile circle.  How did they build this?