score:8
I can think of at least one place where it would have been common.
Roman infantry were typically equipped with short-swords which they used once combat got down to hand-to-hand. Of course their opponents weren't typically from rich empires that could afford standard swords for everyone, but in the case of the Persians it was close.
Persian armies seem to rely much more on cavalry, and much of their infantry was either archers or spear-wielding rabble, but they did typically have Daylamite units of elite heavy infantry that used much the same equipment package as the Roman infantry.
So when Rome fought Persia (which was pretty often), and legions got into hand-to-hand action with Daylamites, there would have been sword-vs-sword fighting.