The economic and political challenges along the maritime borders of the Roman Empire were multiple.The North Sea coasts were the focus of the attention of traders within the framework of commercial exchanges, of the General Staff preparing for the conquest of Britain under Claudius, and for the defence of the coastlines from the time that their protection became required. The design of a defensive system and the establishment of a supportive force followed a long path through five centuries, adapting to each development and changing strategy and evolving military installations.It had to face the threat of Saxon pirates, not to mention the use of the Roman fleet for political purposes as under Carausius. Military systems are complex because they rely upon the combination of various elements, ports, fleets – thus the famous Classis Britannica – forts protecting estuaries and watch-towers.This border represents a page in military maritime history, but its coasts, in Great Britain, the Netherlands, Belgium and France, contain archaeological sites of high heritage value that deserve a large audience.