5. c.1250-88 Renaud de Cormont
After 30 years of architectural production Master Renaud, son of Thomas, the previous master, began a phase of critical review and experimentation leading to the introduction of radically new forms. To the west of the upper transept a new kind of lightweight openwork flyer replaced the solid units built by Thomas. Soon afterwards, on the east side of the upper transept this kind of flyer was developed further and the triforium glazed. Continuing experimentation apparent in the upper transept led to final choices in the upper choir with its staccato forms emphasized by gables over each bay of the choir triforium and gables over the exterior clerestory windows. The work was interrupted by a fire in 1258 which left its marks upon the upper choir, particularly in the triforium on the south side. Renaud’s name is recorded in a 1260 contract that designates him as magister fabrice beate marie ambianensis. The axial window of the upper choir is dated 1269; at this date the high vaults of the choir were probably completed and covered with a low-level provisional roof: the existing roof was installed soon before 1300. A central steeple was probably built soon thereafter: it was then possible to vault the main crossing. The pavement was installed under Renaud's direction in 1288.