A hack 'n slash action RPG where you play as a Roman centurion.
Both the story and the gameplay make no attempt to hide they're blatant copies of Gladiator (2000). But it works surprisingly well - the graphics are amazing and the finishing moves on the enemies are spectacularly bloody and gory, as fits the source of inspiration.
And yes, predictably one of the levels of the game takes place in the Colosseum.
Worth noting that there's a whole number of strategy games where you play either as Rome or one of its enemies, but I'm not sure I can name any games where you play as a Roman soldier, other than this.
As such, definitely one for the preservation program.