The Norman Chapel is the oldest accessible part of the castle built about 1078. Its architecture is Anglian in nature, possibly due to forced Anglian labour being used to build it. In the 15th century, its three windows were all but blocked up because of the expanded keep. It thus fell into disuse until 1841 when it was used as a corridor through which to access the keep. During the Second World War, it was used as a command and observation post for the Royal Air Force when its original use was recognised. (The Cathedral was targeted for a Baedeker Blitz or bombing raid by Germany but escaped because fog rolled in and blocked the pilots' view.)