 The walls were made in groups, by groups of gangs, which explains the different textures as you walk along the outer perimeter.The Saxon Shore forts, including Portus Adurni, were built during the mid to late 3rd century amid increased instability in north-eastern Gaul and the Rhineland, eventually leading to the Roman evacuation of that area.The forts were intended to maintain control over the region, and monitor shipping and trade, as well as defending against raids from across the English Channel.