Ireland, Scotland, the Isle of Man, Wales, south-western Britain (Cornwall and Devon) and Brittany were the principal Celtic countries in the sixth and seventh centuries, although some other parts of Western Europe still had a Celtic vernacular language at that time. Brittany, south-western England and Wales had all been part of the Roman Empire, though the level of participation in Roman material culture and civic life varied enormously across them and though some parts had frequently had a military presence. Eastern Brittany and south-east Wales had been more affected, and the coasts of Wales, had had forts built and refurbished in the late fourth century. Despite the geographical differences, the economic base in Celtic areas was one of mixed farming, supplemented by hunting and gathering when appropriate. The structure of Celtic societies in the sixth and seventh centuries is also complicated by the migration factor and its uneven operation, as are societies in so many other parts of Western Europe.