So it was that, rotting from within with loathing and bitter spite, the iron facade the Legion presented to the Imperium obfuscated the extent of how rapidly and how deeply it had descended into homicidal madness, until at last it was called on to help in the punishment of the rebellious Warmaster Horus at Istvaan V, and the dark truth was revealed. Perturabo arrived at Istvaan V in the wake of the bloody pacification of his homeworld of Olympia, a campaign that wiped out the entire population, and some claim tipped Perturabo and his Legion over the edge of madness and fully into the abyss of betrayal during the subsequent Drop Site Massacre, an infamous action that will echo forever in the history of the Imperium. In the wake of the Drop Site Massacre, Perturabo left the blasted carcass o