[From the back of the case (US PS2 edition)]:
Cortez is back and this time he's bringing some friends to help him fight the past in order to change the future.
Fight across multiple time period in Story, Arcade, Co-op, and Multiplayer modes.
8-player online multiplayer battles—choose from 16 maps or create your own.
Arm yourself with a massive arsenal of weapons from the past, present, and future.
Innovative time travel gameplay lets you team up with your past or future self and be your own ally.