My ancestry is German and English, so I'd guess I'd be fighting the Roman Army as a Germanic Barbarian. Or perhaps dishing it out with France as an English soldier during the hundred years war. Maybe even, and pls don't hate me for saying this, fighting against the Americans in the War of 1812 (although I might be on the Canadian end by that point).
Really, when it comes down to it, once you have an idea of your ancestry, you can only chase it back so far. Who knows what your ancestors werre past that? Maybe your ancestors were knights, or maybe an equivalent of Roman Special Forces, maybe they dug tunnels for the Underground Railroad or were revolutionaries who either had their ideas stolen or never lived long enough to spread their ideas.
But to me, fighting the Romans with guerilla tactics and getting up-close and personal (and winning) would be kind of fun. An interesting experience, at least.