Like that of the town, the origin of the town’s fortifications remains unclear. The original walls didn’t extend very far and only included the immediate vicinity of the cathedral (Tour-du-Chastel). It probably only consisted of fences attached to a few posterns. It extended east towards the Odet and Frout rivers. To the west, it included only part of rue Keréon and rue du Guéodet. The main entrance of rue Keréon named Portz Men (stone door) was topped by a watchtower. A second opening existed on rue du Guéodet.

By the 14th century the town had left its early Middle Age setting. A stone rampart with battlements, topped by a walkway, followed on from the first enclosure under the reigns of Duke Jean I le Roux (1237-1286) and Jean II (1286-1305). The medieval city of Quimper was surrounded by 1500 meters of walls bathed by the Frout, Odet and Steir rivers. To the north, large 15 meter moats protected the ramparts from land attack. These high walls were protected at intervals by defence towers. The most imposing of them, the Tourbie or Bihan tower or Bizien also served as a home for the Governor until the 16th century. With a diameter of 18 meters, its walls reach a thickness of 4 meters. A single tower still exists today : the Nevet tower. It carries the traces of the 14th and 15th centuries, in its lower part two gunboats were organised in the 15th century for adaptation to artillery work. Here we can imagine just how important the fortifications were which are no longer present.

A few sections of the ancient ramparts still exist. A portion once bordered by the Odet extends from the ancient bishopric until where the Pennalen tower used to stand. On rue de Juniville, another piece of wall was exposed during the drilling of a road. Towards rue des Douves, a portion of ramparts surrounds the town’s last defence tower. Another imposing section of rampart serves as a fence at the Tour d’Auvergne secondary school on place de la Tourbie. Lastly, all along the Pichery pedestrians can see a few pieces of wall on which residential homes have been built.

Six fortified gates allowed entrance to the town. Near the Tourbie, a gate with a drawbridge received travellers coming from Briec, Châteaulin or Brest. The Saint-Catherine, Saint-François, Médard, Saint-Antoine and Reguaires gates completed the plan. In troubled times, only the Médard and Saint-Catherine gates remained accessible. The latter was certainly the most impressive, with its drawbridge framed by two high towers. Médard gate was itself protected by a drawbridge and two portcullis. Near its location there still stands an elegant corbelled watchtower.

A small ducal castle stood at the confluence of the Odet and Steir which allowed the unification of the two watercourses. Its construction experienced many setbacks. In 1209-1210 Guy de Thouars, husband of Duchess Constance of Brittany, started building a fortified house on lands belonging to the episcopal stronghold, thus provoking the Bishop’s ire who then cast a ban on Duchy land. The building was finally destroyed.

Two centuries later (1399) Jeanne of Navarre, wife of Jean IV, also tried to build a fortress at the same place. The Bishop excommunicated the Duke’s officers and cast a ban on the whole diocese. The building site was once again interrupted. The case was even brought against the Pope, without result. In 1452 Duke Pierre II continued work on the fortress’s construction despite the Bishop’s opposition. After numerous arbitrations, the Duke finally saw his right to custody of the walls acknowledged. The ducal castle - also named ‘little castle’ - was finished in 1453 and the Duke also undertook to repair the enclosure wall which was threatening to fall into ruin.