Battle of Gergovia
http://www.unrv.com/fall-republic/battle-of-gergovia.php
The Romans did not win every battle against the Celts. Ultimately they conquered Gaul and more, but not without paying a price.
Are you just being contentious? For some reason the Tuesday Canteen threads seem to bring out persons who hold a peculiar animosity. I find that curious.
No, I'm not trying to be contentious, but I don't consider the Celts the premiere warriors of ancient Europe. I think the Roman legions were. Does that mean they were perfect? No. Check Carrhae, Teutoberg Wald, every battle against Hannibal but Zama,Adrianople and their inability to defeat the Sassanids in Persia. Still, they conquered Europe, including Celtic Northern Italy, Celtic Iberia, Celtic Gaul,and Celtic Britain. So I'd pick them against the Celts, any time.