How did Frankish settlement affect the language boundary in Belgium and France?

The settlement of the Franks in the 3rd and 4th centuries CE played a decisive role in shaping the linguistic landscape of modern Belgium and France. As these Germanic tribes moved into the region, they established a settlement pattern that eventually formed a distinct linguistic frontier.12

In northern areas, such as parts of present-day Belgium, the Franks retained their Germanic language, which evolved into Dutch. Conversely, those who settled further south in Gaul were fewer in number and rapidly adopted the language of the culturally dominant Romanized population, which eventually developed into French.2

This division created a boundary that roughly corresponds to the current divide between the Flemings in the north and the Walloons in the south. This linguistic frontier, which remains largely unchanged today, marks the extreme limit of early Frankish settlement and continues to serve as a significant cultural and administrative divide in Belgium.21