Built from the same red sandstone as Carlisle Castle, Carlisle's cathedral began life as a priory church in 1122 and became a cathedral when its first abbot, Athelwold, became the first bishop of Carlisle. Among its notable features are the 15th-century choir stalls, the barrel-vaulted roof and the 14th-century East Window, one of the largest Gothic windows in England. Surrounding the cathedral are other priory relics, including the 16th-century fratry and the prior's tower.