Duchy of Normandy

The Duchy of Normandy was a former European sovereign state and later a dukedom of France, founded in 911 CE by the Treaty of Saint-Clair-sur-Epte between King Charles III of West Francia and the Viking leader Rollo. Named for its inhabitants, the Normans, its dukes were often also kings of England from 1066 until 1204, following the Norman Conquest. Philip II of France seized mainland Normandy in 1204, though it remained disputed until the Treaty of Paris in 1259. The duchy was permanently united with the French royal domain after 1469, and the title "Duke of Normandy" is still informally used in the Channel Islands to refer to the British monarch.