In the Middle Ages, people believed that light was the very embodiment of God, and they celebrated his presence with the breathtaking splendour of their stained-glass windows. Very little is known about the men who made them. Yet they are still a source of inspiration to modern craftsmen, like those working on the huge unfinished cathedral of St John the Divine in New York. For the first time, a film camera has recorded for Everyman the magical beauty of the great rose windows at Chartres Cathedral from close at hand. And the great composer, Olivier Messiaen , at the organ of the Trinite church in Paris, talks of the special place light and stained glass have in his faith and his music.