Cross posted from Monstrous Beauty
Others may rave about the Chi Rho monogram from the Book of Kells, but for my money, this is the single most impressive piece of illumination from the Middle Ages. This is one of the carpet pages from the Lindisfarne Gospels. It's said that each of the carpet pages in the Lindisfarne Gospels have an intentional error in the knotwork. Good luck finding it.