A page from the Koran stands on one of the pillars by the front entrance to the cathedral. This collectible dates from the Saracen occupation of 831-1072. When the Normans recaptured Sicily, they remodeled the mosque (which itself was based on a 7th century basilica) and saved this one element unchanged. I remember driving past a house on El Monte in Los Altos for a couple of years in the 1990's, which was being remodeled. Throughout the entire process, the front door and a couple of inches of wall on either side remained. Zoning laws encourage this sort of behavior.