The fen­‐basin is located in a region in which material culture had become largely Germanic by the mid­‐fifth century. This paper evaluates the contribution made to an understanding of that process of cultural change by place-­names, archaeology and documentary records. Archaeological evidence indicates little post-‐Roman abandonment of the fenland; the region continued to be inhabited and exploited. Patterns of intercommoning, the Tribal Hidage, and stray pieces of information recorded by Bede and Felix, demonstrate the presence of territorial groups across the whole basin by the mid­‐seventh century in a complex, almost certainly dynamic, hierarchy of subordinate and dominant polities, principalities and kingdoms, some with some Brittonic territorial names and others with names based on Old English elements. Most of the people who gave these place­‐names were like to have been descended from the Romano‐British and prehistoric inhabitants of Britain. Different cultural traditions cannot be identified in their material culture, and many may have been bilingual. Such commonalities together with continuity across the region in structures governing rights of common pasture suggests that it is as likely that some sub­‐Roman polities evolved into sub­‐kingdoms as it is that other polities were created anew. There is nothing so out of the ordinary in such political changes that they might be ascribed to the influence of incomers. The influence of migration on the evolution of early medieval fenland culture remains enigmatic.