Fortress Britain analyses the security problems faced by the inhabitants of the British Isles. Defending the islands has been a difficult task and they have been invaded by successive waves of Celts, Romans, Germanic tribes, Vikings, Normans. These conquerors, in turn, had to secure their lands against the next emerging enemy. So, archaeology shows that fortifications were common to all groups: Celtic hill forts, Roman camps and Hadrian's Wall; Saxon burhs; Norman castles; Henry VIII's device forts; Martello towers; and the 'stop' lines during the Second World War. The book provides the international contexts for a variety of defence policies over several hundred years and the text is reinforced by numerous maps. The story demonstrates the importance of the sea as a medium for invasion and defence. Consequently, considerable space is devoted to naval matters. The Second World War and Cold War receive detailed treatment and the complex threat of terrorism from is also considered.