A good Overview and Informations about the Gladiators Arena you can find also here,check section "Gladiators Arena".
3rd place: 25 000 Experience
2nd place: 50 000 Experience
For the Victory of the Arena you get a Sash of Gladiator and 75 000 Experience
Sash of Gladiator:
— awarded for 1st place in Gladiators Arena event
— blessed (newbie), unlimited durability
— can be used only by it`s owner
— +30 to all stats
— +1 to all regeneration rates
— exists until next Gladiator Arena event.