As I remember it now, this was taught as a bittersweet moment in our history. We united, we were brave and fought a stronger army but still we were defeated and our chief was captured and killed by the enemy.
As a result we were colonized and we lost almost all our Celtic culture (Celtic culture remains present notably in Bretagne — Britain). But we were "civilized" by the Romans. I think this was taught as being a tough but positive thing.
Today I find it interesting to think about how "civilization" spreading if often a gruesome process and how it's seen centuries, if not (in this case), milleniums later.