Book: Crucible Arenas.
ARENA DESIGNATION: Firebase Delphi
LOCATION: Eos Chasma, Mars
When the Cabal decide to hold an area, they dig in deep. It's surprising, then, that the tunnel system at Firebase Delphi is woefully incomplete by Sand Eater standards. One theory is that it was built simply to be inspected, to satisfy some commander's lack of progress on another front. Perhaps the Cabal simply cut their losses once they realized that the location of the base was sub-optimal, although half-measures are really not something they're known for. We're talking about a culture that will grind a mountain to dust rather than build around it.