Movies with good epic battles

Having just watched Spartacus, I was amazed by the sheer number of people they had during that last battle (and this was in the 1960's, way before CGI, which meant every person out there moving was an actual person), and got me to thinking, "what other movies have battles where two or more armies just converge on each other and fight to the death?"

And on that note, what movies have you seen where there's people (aliens, monsters, etc.) in large numbers just rushing at each other? I'm interested to see what happens in the movie, why that battle took place, and the results of it (because hopefully there's a good reason for that battle taking place, and not just "having a big battle for the sake of having a big battle").

For example, in Spartacus:

Spoiler:

He's fighting because he's tired of being a slave, and wants to eliminate slavery. The Roman Republic, however, is highly dependent on slavery, and won't let someone as lowly as a slave run amok and create chaos in their society, hence why they keep sending army after army against him, despite his ability to win against the Romans until that last battle.

You can see why Spartacus wants to fight, because he's tired of watching men treat other men like their nothing more than animals. It's just too bad the Romans don't see it that way, despite their "advanced" society. And their over-reliance on slaves will be one of their undoing hundreds of years later.

I like how the Romans are largely depicted as the "bad guys", because most other things I read/watch about them usually show them as the "good guys" bringing civilization and order to "barbarians", but from a slave's point of view, Rome is a terrible master.

The battle can be a depiction of a real historical event, or just a made up one if it's cool (kind of like Lord of the Rings).

In this case I'm looking more for older movies (that haven't used CGI extensively that is, so as to rule out stuff like "Lord of the RIngs" or "Chronicles of Narnia" for example, but feel free to list one you think is worth watching), what battle specifically (use spoilers preferably).

The battle can also use any kind of weaponry, whether it's melee weapons or guns. It can even be vehicular combat (like a Star Wars space battle) if it's cool enough (and on that note, anyone have a recommendation for a good tank on tank battle/movie?). And if it's animation, that's also acceptable (here come the anime recommendations hehe, which is fine with me as well).

So, what cool battles from which movies have you seen?

Jam it back in, in the dark.