Built to defend the country against invasion from Napoleon's navy, the Royal Military Canal zigzags from Folkestone in Kent to Hastings in Sussex. It passes by the Cinque Port of Hythe, across the smugglers territory of Romney Marsh, through the ancient ports of Rye and Winchelsea, ending at the shifting shingle of Cliff End. Travelling the length of the route, Shaun Williamson discovers how the need to protect and defend the nation shaped the lives of the common people living on the edge of Britain, during some of the toughest times in our history, from well before 1066 to the present day.