This former collegiate church, a UNESCO World Heritage Site, was begun in the Romanesque style around 1150, but the nave and transept are Gothic and the chancel was rebuilt (late 12C-early 13C). The austere façade, mirrored in the waters of the Canal du Mau, is particularly impressive. The nave sports a set of stained-glass windows, typical of the Champagne region (the finest, in the north aisle, are 16C).