The identity of the inhabitants of the northern Netherlands, before as well as after the 4th century, must to a large extent have been defined by their involvement in one or several networks with a social, cultural or political character. What defined their ethnic identity is unknown. It was probably based on intangible cultural elements, such as more or less mythical stories about their descent, and not on aspects of their material culture such as the style of their pottery. Nevertheless, the events that took place in the 4th and 5th centuries in the northern Netherlands coastal area do suggest that in this case, pottery was an important aspect of at least cultural identity. The decoration possibly played an important role; it spread within a cultural network where its meaning was understood. This same network prevented the remainder of the population of the Groningen terp region from social isolation when a large part of the terp region was abandoned around AD 300. The cultural network clearly functioned as a social network as well. That implies that the people of this area must have identified themselves somehow as being part of this socio-cultural network. We can call this network ‘Anglo-Saxon’, but whether they considered themselves ‘(Anglo-)Saxons’ after this network, or ‘Frisians’ on the basis of old stories about their origins, we do not know. The new inhabitants of the terp region were later called Frisians in historical sources. That may be taken to indicate that the name was associated with the geographic region, and was adopted by the newcomers, or that the name was given to the new population by the Franks, who knew the name from older written sources (Bazelmans 2002; 2009). Another possibility, which is not unlikely in the light of the above, is that the name was kept alive by the small remaining population, which apparently considered themselves Frisians, or by migrants who did not try their luck in the collapsing Roman Empire, but only moved within the Anglo-Saxon area. In any case, it indicates that ethnic identity is something fluid that may be reinvented over and over.