The Battle of La Roche-Derrien was one of the battles of the Breton War of Succession; it was fought in 1347 during the night between English and French forces. Approximately 4,000–5,000 French, Breton and Genoese mercenaries (the largest field army ever assembled by Duke Charles of Blois) laid siege to the town of La Roche-Derrien in the hope of luring Sir Thomas Dagworth, the commander of the only standing English field army in Brittany at the time, into an open pitched battle.