Book: Crucible Arenas.
ARENA DESIGNATION: Bastion
LOCATION: Meridian Bay, Mars
Thick, rugged terrain masks one of the largest Vex structures on Mars, leaving this imposing gate as the only conventional entrance. With the Cabal's interest in Vex activity, it was a matter of when, not if, they would set their sights here.
The Cabal deployed a massive ground and air offensive to breach the wall and enter the subterranean labyrinth. We don't know what the Vex deployed in defense, but we know this: the Cabal didn't make it very far.
The Vex have since mysteriously vanished from this region, giving the Crucible one of its largest arenas in the solar system. The Cabal, on the other hand, still prefer to keep their distance.