Fortifications

A twin-towered gateway, defended by a drawbridge with carriage and pedestrian doors, once led to Mordelles. This symbolic gateway was the place where the future dukes swore their allegiance to Brittany's freedom. To the west, the mediaeval enclosure was built over the layout of the 3rd-century wall. The gateway to the town was protected by an artillery platform built on a walled outwork (or barbican).

Adjacent to the former Hôtel d'Artillerie, Duchesne Tower forms part of the defence wall rebuilt in the 15th century, which extends as far as the Portes Mordelaises. The site's ancient past was revealed by the discovery of a piece of the Gallo-Roman wall, built in the 3rd century to protect this part of the town.