The Celts didn’t need to conquer the Viking by invasion - they did so (in a way) through the kidnappings. The Vikings favored the lovely hardy red-haired lasses they encountered and took them home to breed... many Vikings had Celtic mothers and were raised by them, not their absent fathers.
So I’ve been told. :)
At last! An opinion totally devoid of bias! Something much needed on this forum!
LOL!