User blog comment:James12708/Reapers VS. Forerunners VS. Angels from Darksiders VS. Humanity from Halo VS. Council and humanity from Mass Effect VS. Imperium of Man/@comment-3228423-20130124224540/@comment-4967682-20130125060527

You assume length matters?

You truly have no idea how powerful that universe is. An Imperial Battlecruiser is about the size of a Covenant one. The problem? The battlecruiser could easily take and dish-out gigaton level damage, something no ship in the entire Halo universe has. Remember those small turbolasers dotting the Star Destroyer? Every one of those guns had a destructive power of 200 gigatons.

See also this thing http://starwars.wikia.com/wiki/Acclamator_I-class_assault_ship, the predecessor to the Star Destroyer, which was half the size and "only" had eight turbolasers, each of which had the firepower of 200 gigatons.

There's no way that any UNSC or Covenant or Council or Reaper fleet could even come close to scratching a ship capable of taking hundreds of gigatons of force. The Galactic Empire would be a better match for the Forerunners.