The Portes Mordelaises are Rennes' most evocative piece of medieval fortification: a double-towered gate, drawbridge passage, and short stretch of rampart just west of the cathedral. For centuries this was the formal entrance used by the dukes of Brittany before their coronation ceremonies, which gives the gate more weight than its modest footprint suggests.
Come here while walking the old centre rather than treating it as a standalone excursion. The stonework, towers, and restored wall-walk make a good contrast with the half-timbered streets around Place des Lices, and the gate helps explain how compact, defended, and ceremonial medieval Rennes once was.