This is a Halo 3 remake. Really popular map, now recreated in Reach. The map does not feel exactly the same, but the concept is.
Here is a link to the Forgehub post. With pictures and links!
http://www.forgehub.com/forum/reach-casual-maps/129765-gladiator-arena.html
Also, quick shout out to a forger named WARHOLIC. He also created a similar version of this Gladiator on Arena, but his map supports up to 16 players, while mine only supports up to 12. Really nice map.
Check his out here.
http://www.forgehub.com/forum/reach-casual-maps/134190-coffin.html