Château de Saint-Aubin-du-Cormier: A Medieval Breton Frontier Castle
Site at a Glance
- Rating
- 4.3
- Popularity
- Low
- Country
- France
- Primary era
- Medieval
- Eras represented
- Medieval
- Civilizations
- Duchy of Brittany
- Site type
- Military
- Remains
- Castle
On this page12 sections
History
Château de Saint-Aubin-du-Cormier is a medieval castle in France, built by Breton rulers in the thirteenth century on the Marches of Brittany, the duchy’s northeastern frontier zone. In 1225, Peter I, Duke of Brittany, ordered its construction to defend the frontier and contain the powerful lordships of Rennes, Vitré, and Fougères. The castle stood near the Forest of Rennes, above a broad and fertile valley, at a site where a chapel dedicated to Saint Aubin already existed.
Thirteenth-century frontier fortress
After the death of Louis VIII of France, Peter I changed allegiance and fought alongside Henry III of England. In 1231, the army of Louis IX, king of France from 1226 to 1270 and later known as Saint Louis, unsuccessfully besieged the castle. Peter surrendered it in 1234 after submitting to the French king.
Succession conflict and rebuilding
The castle became involved in the War of the Breton Succession, a fourteenth-century civil conflict between the Blois and Montfort factions over the Breton ducal succession. Charles de Blois captured it in 1342, and it was handed over to Jean IV de Montfort in 1381, after he became duke of Brittany.
Further changes followed in 1430, when the castle was remodelled and fortifications were erected around the town. In 1458, Artus Brécart became captain of Saint-Aubin-du-Cormier. He was a Breton nobleman and military officer who served Duke Arthur III, and he also held the offices of Constable of Rennes and captain of Mervent and Coudray-Salbart. His marriage to Jacqueline of Brittany, Arthur III’s daughter, connected him directly to the ducal family.
The Battle of 1488 and dismantling
In the late fifteenth-century Mad War, a conflict in which Brittany and several French nobles opposed the authority of the French crown, the French army commanded by Louis II de La Trémoille advanced from Nantes after taking Fougères. It confronted the Breton army at the Battle of Saint-Aubin-du-Cormier in 1488. Duke Francis II of Brittany was defeated, and approximately 5,000 to 6,000 Breton soldiers and 1,500 French soldiers were killed. The defeat quickly brought about the capitulation of the anti-French coalition.
Under the Treaty of Verger in August 1488, Francis II recognized himself as a vassal of Charles VIII of France, and the castle was given as security to the French king. The treaty marked the end of Breton independence. Charles VIII ordered the castle dismantled in 1490 because it could have served as a point of resistance and because it represented the authority of the Breton ducal state. The work was probably carried out by the Lisières de Bretagne, an artillery force of 6,000 infantrymen and 400 men-at-arms, supported by at least 20 specialist gunners and 31 guns. The same force destroyed the fortifications of Dol.
The dismantling removed the fortress as a defensive position while also preserving the memory of its political importance. Local tradition says that the keep was mined and split in two, with its eastern face left standing to humiliate the Bretons. Surviving evidence instead indicates that mining reduced the keep by roughly half its height and that the surviving face is the northern one. The castle was later abandoned.
Legend and modern protection
A nineteenth-century romantic legend claims that Anne of Brittany witnessed the battle, escaped from the castle through an underground passage after the Breton defeat, and confused her pursuers by having her horse shod backwards. The story also says that her servant betrayed her and was later killed. This account is legendary, and Anne was elsewhere at the time.
The castle’s two enclosures were entered on the French register of historic monuments in 1926. Orders issued in 2017 and 2025 replaced that protection, while a 2026 classification as a historic monument partially superseded the 2025 registration.
Remains
The castle occupied a hill or ridge overlooking a broad valley near the Forest of Rennes. Its fortified plan formed a quadrilateral approximately 90 to 100 metres long and 30 metres wide. Ten circular towers flanked the enclosure, while the keep stood at the southwest corner. The keep is now the sole surviving structure, and it remains in ruins.
Fortified enclosure and keep
Quadrilateral enclosure
The enclosure organized the castle around a broad, elongated quadrilateral. Circular towers strengthened its sides, and additional fortifications surrounded the town after the remodelling of 1430. The castle’s location above the valley formed part of its defensive setting, while the earlier chapel dedicated to Saint Aubin occupied the site before the fortress was built.
Surviving keep
The keep, or donjon, was the principal fortified tower of the castle, combining defensive, residential, and administrative functions. Its walls are 3.5 metres thick. The tower originally rose through five levels to approximately 15.5 metres, but the dismantling of 1490 reduced it to about half its former height. Only the northern face survives; the other parts of the castle have disappeared.
Interior levels
Lower and entrance levels
The ground floor was completely windowless. The first floor contained the entrance level, a fireplace, and a window fitted with stone side-seats, which were built into the thickness of the wall. Another fireplace incorporated an oven.
Upper levels and wall-walk
Latrines occupied the second floor. The third floor probably belonged to a fourteenth-century addition and contained a wall-walk, a passage along the top of a defensive wall. These surviving details show how the keep combined enclosed lower spaces with facilities for occupation and defence.
