There is an account of the early celts using swords against leather armor when they had chainmaille. When their enemies adopted chainmaille they came back with heavier swords similar to hand-and-a-half swords. They had half plate at this time. They always seemed to be one step ahead of their enemies. I think this was in the article by National Geographic in the 70's. I am not sure how accurate this artical was as newer research always seems to change what the first guy thought.