The Church of Saint-Quentin is a Romanesque and Transitional building. The Romanesque church, built around 1200, had a cruciform plan, of which the nave, the transept and its transitional crossing tower, two chapels (southeast and northeast corners), and the upper part of the choir still remain. In the 13th century, the vaults of the chevet, the transept arms, and the other chapels were added. In the 15th century, the lower part of the choir was rebuilt and encircled by an ambulatory and three apsidal chapels. The most extensive restoration followed the bombings of World War II and was completed in 1968.
The Romanesque façade, flanked by two corner turrets, is composed of three levels crowned by a triangular gable. The first level features a neo-Romanesque portal, the second features three large round-arched bays in front of a passageway, and the third features small Romanesque windows, alternating between blind and openwork. The crossing is surmounted by a squat tower crowned with a pyramidal spire. The tower is flanked by four octagonal corner turrets with pinnacles. The nave rises over three levels, divided by five bays. The higher one ascends, the larger the openings become, and the more light enters the building. The nave has a flat wooden ceiling. The projecting two-bay transept features two bays topped by a large oculus. The arms of the transept are covered with vaults.
The choir has one bay and seven sides. It is vaulted in white stone and is surrounded by a late Tournai Gothic ambulatory with large bays under an archivolt. The latter is crowned with ribbed vaults made of Tournai stone. Note the polychrome vaults of the axial chapel, dating from the 15th century and depicting the four evangelists accompanied by angels, as well as the marble enclosure separating the choir from the ambulatory.