The bell towers of the Collegiate Church of Notre-Dame-et-Saint-Nicolas are pierced with two levels of arched bays adorned with railings and topped with a square dome and a polygonal lantern surmounted by a globe and a cross. They dominate and protect the Cité Vauban, the church having been deliberately built on the most exposed bastion of the fortified enclosure to dissuade the enemy from bombarding a religious building.