When did the Duchy of Brittany exist?

The Duchy of Brittany existed 10th century–1532. On this map it is drawn AD 947–1187, 1206–1428, 1440–1491.

How large was the Duchy of Brittany?

At its greatest extent drawn on this map, the Duchy of Brittany covered about 37,000 km². That is the largest area the border data gives it across the years it is drawn, not necessarily its greatest extent in history.

Europe · The early medieval west

Duchy of Brittany

10th century–1532

Duché de Bretagne; Breton Dugelezh Breizh; Latin Ducatus Britanniae. Principal seats: Rennes and Nantes.

See it on the map → Wikipedia ↗

Existed: 10th century–1532
Shown on the map: AD 947–1187, 1206–1428, 1440–1491 (3 periods)
Peak area: 37k km²
Region: Europe

Names

Duché de Bretagne; Breton Dugelezh Breizh; Latin Ducatus Britanniae. Principal seats: Rennes and Nantes.

Development

A duchy from the 10th century, ruled by Breton comital houses (from 939) and drawn between the Angevin/Plantagenet and Capetian spheres; the Angevins controlled it until 1204. The Breton War of Succession (1341–1365), an offshoot of the Hundred Years' War, pitted the House of Montfort (English-backed) against Penthièvre/Blois (French-backed); the Montfort claimant prevailed at Auray (1364), and the Treaty of Guérande (1365) confirmed John IV, stipulating that failing a Montfort male heir the Penthièvre line would succeed. Brittany maintained quasi-independence with its own Estates and coinage.

Union with France

Duke Francis II died in 1488 (after the French–Breton War of 1487–1491), leaving his daughter Anne of Brittany. Charles VIII had her proxy marriage to Maximilian of Austria annulled and married her (1491); on his death she married Louis XII. The duchy passed to her daughter Claude, whose husband Francis I incorporated it by the Edict of Union of 13 August 1532, ratified by the Estates of Brittany, preserving Breton privileges.

Common questions

What was the Duchy of Brittany?: Duché de Bretagne; Breton Dugelezh Breizh; Latin Ducatus Britanniae. Principal seats: Rennes and Nantes.
When did the Duchy of Brittany exist?: The Duchy of Brittany existed 10th century–1532. On this map it is drawn AD 947–1187, 1206–1428, 1440–1491.
How large was the Duchy of Brittany?: At its greatest extent drawn on this map, the Duchy of Brittany covered about 37,000 km². That is the largest area the border data gives it across the years it is drawn, not necessarily its greatest extent in history.

Sources

This compendium cites its sources once for the whole document rather than per territory. Its bibliography names the English Wikipedia articles for each territory as the primary basis, cross-checked against Encyclopædia Britannica and specialist snippets, and flags entries built on unreliable foundations — the 911 treaty of Saint-Clair-sur-Epte known only from Dudo of Saint-Quentin, and Arnaud Amalric's alleged order at Béziers attested only decades after the fact. The article this entry is anchored on:

Wikipedia — Duchy of Brittany en.wikipedia.org/wiki/Duchy_of_Brittany

This entry was last updated 27 September 2026.

This entry was researched and drafted with AI from the sources above, and has not been reviewed by a historian. How entries are made

Text available under CC BY-SA 4.0: reuse it with a credit to The World Through Time and a link to this page. Passages drawing on the Wikipedia articles listed above are also licensed CC BY-SA 4.0 by their contributors.

Border geometry for the map itself comes from Cliopatria v0.12 (Seshat Global History Databank, CC-BY-4.0).

See the Duchy of Brittany in its world

Open the atlas at 1067 and every neighbour, rival and successor is on screen with it — then drag the slider and watch what happens next.

Open the map at 1067 →