The far west of Brittany, once a semi-independent viscounty, broken by Henry II and Duke Geoffrey after 1179, when much of it (Morlaix above all) passed into ducal hands.
What remains to the house of Léon is the coast from the Aber country to the Élorn, with Landerneau, La Roche-Maurice and Brest. They are Arthur's partisans.
Who he is
- Name
- Guyomarch V of Léon (Guihomar), with Conan, who follows him in the viscomital list
- Title
- Viscount (lord) of Léon
- Since
- After the death of Guyomarch IV in 1179
- Born
- Not pinned
- Family
- Sons of Guyomarch IV (died 1179). Conan fought for Arthur and was captured with him at Mirebeau in 1202; whether he is Guyomarch's son or his nephew is not pinned here.
- Confidence
- medium
Viscounty of Léon article: Guyomarch V (died after 1216) 'controlled only a small portion of Léon' and sided with Constance and Arthur; large parts of the viscounty were ducal from 1179 to 1269.
Overlord
The duke of Brittany
What it holds
- Landerneau and La Roche-Maurice on the Élorn
- Brest castle and port (held by the viscounts until 1240)
- Lesneven and the coastal pagi of the Léon (with wreck rights, a notorious Léon revenue)
- Saint-Pol-de-Léon is the bishop's city
How it was acquired
Hereditary; reduced after 1179.
Allies and rivals
Partisans of Arthur; rivals of the ducal officers at Morlaix.
How things stand that morning
Hold the residue of Léon; the duke holds Morlaix. Quiet.
Wealth
Wreck rights (the 'brefs' of Léon), fisheries, the port of Brest, cattle.
Military
Castles of Brest, La Roche-Maurice and Landerneau.
Threats
- Further ducal encroachment
Places of note
- Brest: Castle and port
- La Roche-Maurice: Castle on the Élorn
- Lesneven: Town
Where the sources disagree
Evidence: The division of Léon after 1179 is attested in outline only.
On the map: Approximate; the ducal share of Léon after 1179 was larger than Morlaix alone, but its limits are not pinned.
Primary sources for Brittany
Chronicles, registers, sagas and inscriptions written in or near 1200 that cover this entry. Each has its own page with editions, translations and where to read it.
- Chronicles of the Churches of Anjou (Saint-Aubin, Saint-Serge, Saint-Florent and others), Various (monks of Angers and the Loire) (11th to 13th centuries; the Saint-Aubin annals run to the 1220s). The Angevin houses' own annals of the succession crisis in their city: Arthur received at Angers in 1199 with Constance and the Breton and Angevin barons, John's counter-moves, the defection of William des Roches and the Angevin lords to John, and the peace of 1200 that left Arthur John's vassal. Read online
- The Great Chronicle of Tours, Anonymous (a canon of Saint-Martin of Tours) (about 1227). The Loire valley's view of the Angevin succession. Read online
- History of the Dukes of Normandy and the Kings of England, Anonymous of Bethune (a clerk in the household of Robert VII of Bethune) (about 1220). A Flemish lord's clerk writing twenty years on, with a soldier's interest in who fought whom. Read online
- The Acts of Philip Augustus, with Delisle's Calendar, Various (the French royal chancery) (1179 to 1223). The king's own charters and treaties for the year: the peace of Peronne with Baldwin IX in January 1200, the treaty of Le Goulet with John on 22 May 1200, the marriage settlement for Louis and Blanche, the privilege for the scholars of Paris, grants to towns, abbeys and Norman lords, and the first acts of the king's new acquisitions in the Vexin, Evreux and Berry. Read online
Sources and studies
Last revised 4 November 2026. Published 4 November 2026. Suggest a correction on the OMNIA Discord.