Not sure about Gladiator, but often you'll just get a dozen or two people and then shoot the same shot with those people in different places. You then composite the shots together so they appear to fill the area.

I was actually surprised recently when I saw an FX guy's showreel of TV clips and for a TV shot in a prison canteen they composited about a dozen guys into the background in multiple places rather than drag in a few more extras. I guess extras must cost a lot more than FX these days :).

I saw a special on the Phantom Menace and they used colored cotton ear-swabs for some crowd scenes. It didn't sound like they changed it in post and I didn't notice anything as the pod racers zipped by. I can only assume the background blurred with the fast motion. Still it amazed me, Lucas uses a SFX team when he takes a dump yet he did that bit pretty old style.

RJSchwarz
San Diego, CA

I'd just grab a big group of friends. ITs easier, unless you're like me and don't have friends...

You people have held me back long enough, I'm going to clown college!

In Gladiator they filled a pie-slice section of the stands with extras and then just duped that section next to itself over and over until they filled the entire pie. With an arena the stairs/aisles make a nice break between sections.

This should work with a modern sporting event as well. Still means a lot of extras but you don't need thousands and thousands.

RJSchwarz
San Diego, CA