Many thanks for your fast and informative response, Ahtaswintha! I am trying to figure out who would have been where as the Rhine-Danube limes gradually pushed forward in the Claudian to Hadrianic periods to the final, essentially static positions they occupied from 150 to 260 ce. The position of the fortifications at different time periods is nicely illustrated by the map in Rabold, Schallmayer and Thiel but what it does not show is the existing civilian infrastructure over which the military frontier progressed.

I agree that, at the start of this process, the changes wrought by the Gallic War would only have had a few generations to bed down, but I am imagining a mixed Germanic-Gallic, slightly Romanised population with considereable traffic both ways across the border.

Britta Rabold, Egon Schallmayer, Andreas Thiel Der Limes. Die Deutsche Limes- Straße vom Rhein bis zur Donau Theiss, 2000. ISBN 3806214611