This cathedral came into being in the 14th century when two perpendicular churches were joined together. The nave of Saint-Etienne, which was built in the 13th century, was opened up and attached to the north side of a Romanesque church dating from the 10th and 11th centuries.In the 15th century, a transept and a choir were added to this new nave. The windows and the open triforium, which take up two-thirds of the wall space, have remarkable stained glass windows made, in particular, by the master craftsmen Hermann de Munster (14th century) and Valentin Bousch (16th century). Their work was complemented in the 20th century by stained glass windows designed by the painters Marc Chagall and Roger Bissière.