In the Middle Ages walls and ditches were used for defensive purposes on land; city walls and moats surrounding castles are part and parcel of the public image of the Middle Ages. Less well known are the defence systems constructed under the sea to protect harbours and waterways. In Scandinavia such systems, ship-blockages, are especially well investigated in Denmark. In Norway medieval harbour-defence systems and ship-blockages are less known. This paper presents and discusses medieval harbours and defence systems in Norway, in particular the newly discovered jetty and possible ship-blockage on Veøy in Romsdal, western Norway.