The Britons were a Celtic people who inhabited Britannia from the British Iron Age (800 BC) until the 11th century, by which time the Britons had split into distinct ethnic groups such as the Welsh in Wales, the Cornish in Cornwall, the Bretons in Brittany, and the remnants of the Picts in northern Scotland. The Celts spread from a Central European homeland into France and, eventually, into the British Isles in either a large-scale migration or invasion. The Celts introduced a hillfort society to Iron Age Britain, and the earlier inhabitants of Britannia were assimilated into the new Celtic Brythonic culture. The Celtic Britons were the dominant group in Britain until the 1st century AD, after which the Roman conquest of Britain led to the creation of the Romano-British culture and Romanization. During the 5th and 6th centuries, in the aftermath of the Roman abandonment of the British Isles (Sub-Roman Britain), the Britons briefly returned to ruling Britannia alongside the Romano-British elite, but the Germanic Angles, Saxons, and Jutes went on to invade England during the late 4th and early 5th centuries. While the Britons (led by warriors such as King Arthur) stiffly resisted the Saxons at the Battle of Mount Badon and other engagements, they were gradually forced back into northern England, Wales, and South West England as the Saxons established the kingdoms of Mercia, Wessex, East Anglia, Sussex, Hwicce, Northumbria, and others. For this reason, Wales and Cornwall became strongholds of Celtic/Brythonic culture for centuries, while the rest of England adopted Germanic culture. Many Britons also fled to northern France (Brittany), the Channel Islands, and Galicia (hence the village of Bretonia in Lugo). By the 11th century, the Britons ceased to be a united culture, instead fragmenting into smaller Celtic culture.