The pictures were all taken under urban guerilla conditions, and so are not as detailed, perfect in colour, crispness and verticality as those ones which appear in beautiful art books, but they probably give a better impression of what people, medieval or other, actually saw. That leads to a few thoughts on their function. The traditional take on this is that they were essentially didactic, providing lessons to the illiterate. Hmmm.
The first time I visited Chartres cathedral, I thought initially it must not be open to visitors as it was pitch dark inside. Then it became apparent that there were people in there, and my husband and myself were both mystified as to why there were no lights on. It was a very bright day outside and we had to stand for about 15 minutes until our eyes adjusted before we dared tackle navigating around. And then something extraordinary happened. The whole place just started to shimmer with colour, constantly changing as the light changed behind the heavily coloured 13th century windows. It looked nothing like a picture in a book, but one can only imagine the impression on the citizens of medieval Chartres, which was probably as dingy and smelly as most medieval cities outside the cloisters. Add all the colour and gold which has been scrubbed off the interiors of medieval churches in modern times and the whole impression must have been dark and colourful, shiny and aromatic, and alive; maybe a glimpse of Paradise.