One of the largest early Gothic buildings. It is likely that building began ca. 1140 (Henriet). The south chapel was in use by 1151 and Pope Alexander II (reigned 1061-1073) dedicated the altar of SS Peter and Paul on 19 April 1164, which indicates that the liturgical choir was roofed and vaulted. The building was nearing completion in 1168. Most of the west façade must post-date the fire in the city of 1184. The chapel of St Michel in the north-west tower was dedicated in 1210, that in the south-west tower in 1221 (rebuilt after a collapse, 1268-1290). The main vessel is extremely wide (16 m) and, for its time, tall (ca. 26 m). The sense of scale is reinforced by the huge domical, sexpartite main vaults. The most profound changes began in 1490 with the creation by Martin Chambiges of new transept façades and a regular crossing, starting with the south transept arm.