Although it came to be subsumed within the Hundred Years’ War, the ‘Combat of the Thirty’ was really a conflict of the Breton War of Succession, a struggle between the the House of Montfort and House of Blois for control of the Duchy of Brittany. The House of Blois was led by Charles of Blois, who received support from the King of France; the House of Montfort was led by John de Montfort, a French noble with the backing of the English king Edward III. By 1531, the Breton conflict had reached a virtual stalemate. Each side controlled several castles throughout Brittany, and each made the occasional sortie against the other.
In early 1531, Jean de Beaumanoir–a captain over a castle held by the Blois faction– challenged Robert Bemborough to a personal duel. Bemborough, an English knight in charge of a Montfortist faction, suggested expanding the duel into a larger conflict, and in the end it was agreed that thirty knights from each side would meet in combat.
The cause of the conflict is an issue of debate among historians. The medieval chroniclers of the Combat of the Thirty portrayed it as a shining example of the chivalric code in action. Other accounts of the combat, however, portray the combat as Beaumanoir coming to rescue the the defenceless local population from the ruthless control of Bemborough and his Montfortist knights. This latter account can be viewed skeptically, though, because it was written by a local supporter of the Blois faction.
Regardless of the cause, we know the details and result of the Combat of the Thirty that occurred on 26 March 1351. The combat took place at the Halfway Oak between Ploërmel and Josselin, and was arranged to be fought as a pas d’armes. Hand-selected combatants–thirty on each side–fought in front of a large crowd that had organized the event as a tournament. After a battle that lasted several hours and was fought with gallantry by both sides, the largely English force led by Bemborough was defeated. Bemborough himself had been killed, possibly by Beaumanoir, and eight other of the English knights had also been slain. Despite the enduring fame of the two main figures in the Combat of the Thirty, it had no substantial effect on the Breton War of Succession.