The chapel has a flat chevet and two circular towers. The choir has five crossings and ten side chapels and terminates with a rectangular chevet. Surrounding the ambulatory may be a ring of chapels called a "chevet". In the 15th century, the Gothic "chevet" of the cathedral was reconstructed. In July 1221, the chapel of this axially-radiating chevet entered use. A transept and three apses replaced the earlier chevet. The south polygonal chevet of aisles were built as the first ones. The 1958 excavation uncovered the 1359 additions, including the chevet apse. The cathedral chevet opens onto the ambulatory through two arches. At the eastern end of the cathedral we come to the apse or the chevet. The chancel has a flat chevet and is also barrel-vaulted. The east end is a chevet of nine radiating chapels connected by an ambulatory. The Chevet preserves the structure of the walkway between the two Bartizans. The chevet end displays fine marble altars and magnificent stained glass windows. The chevet has a small door called the "Porte de la Vierge".