This is a great thing to put next to e.g. voting maps, language, religion, etc - https://www.reddit.com/r/phantomborders/ https://www.reddit.com/r/phantomborder

This is a great thing to put next to e.g. voting maps, language, religion, etc - https://www.reddit.com/r/phantomborders/ https://www.reddit.com/r/phantomborders/ is fascinating sometimes. For my part, the Romans never went more than halfway up the Netherlands, meaning the north ("above the rivers") is culturally somewhat different from the south, although the cultures did converge over time. But "below" the rivers is still generally Catholic wheras "above" is Protestant. For example.