Frecoes are, for most of us, an Italian thing. Painting on walls just isn't something we think artists did in medieval France and England.
But that's got more to do with centuries of damp than it has to do with medieval artists' work. Every so often you come across a wall painting that startles you with its vividness - and makes you realise how much we have probably lost.
Amiens Cathedral for instance has a lovely painting of the Sibyls; fashionable fifteenth century ladies, in lovely springtime colours - living green, sweet pink, golden yellows. But look more closely, and you'll see the paint is actually flaking off the wall; how much longer will they be there?
I was amazed recently to find a stunning wall painting in my own city. I never knew it was there. Yet it's of such fine quality that if it were in Florence or Venice, it would be in all the guidebooks.
St Gregory, Pottergate, Norwich, was only open because there was a craft fair inside. Norwich has many fine Perpendicular churches, and at first sight this was just one more of the same style - whitewashed walls, most of the furnishings gone, cobwebs and damp.
Then I saw the painting at the back of the north aisle. St George and the dragon, against the dreamlike parapets of a fantastic castle. Its colours seemed darkened by time but the lines of the painting were still clear.
Maybe it doesn't rank with Uccello. But it's an amazingly beautiful piece of work. It's also a testimony to the medieval culture of Norwich, where St George and the Dragon were part of the guild celebrations (a dragon still turns up to the mayor's procession), and the Guild of St George was one of the most powerful.
Yet this painting is unnoticed, unprotected, in a redundant church that's open a few times a year. And though it's in a better state than the Amiens Sibyls, I wonder how it will fare in future, in an empty church that's used a few times a year.