Event · M30–M31
Virus-bombing of Isstvan III
The virus-bombing of Isstvan III opened Warmaster Horus’s rebellion, annihilating loyalist Space Marines stranded upon the planet’s surface. Ordered by Horus himself, it was the first overt act of the war later known as the Horus Heresy, transforming a nominal campaign of pacification into a calculated purge of those Astartes who remained faithful to the Emperor of Mankind. Elements of the Sons of Horus, World Eaters, Emperor’s Children and Death Guard Legions had been despatched to suppress a rebellion on Isstvan III. Once loyalist companies were committed to the surface, Horus withdrew his own supporters to the fleet and ordered the bombardment of the planet with the life-eater virus, a weapon that dissolved organic matter and left the loyalist forces to die alongside the world’s population. A small number of officers, including Garviel Loken, Nathaniel Garro and Saul Tarvitz, survived the atrocity and the subsequent hunting of stragglers by traitor forces. The massacre revealed Horus’s treachery beyond doubt and set the pattern for the Heresy’s opening campaigns, in which entire Legions were divided between those who followed the Warmaster and those who remained loyal. Survivors of the bombing carried word of the betrayal beyond Isstvan, contributing to the wider galaxy’s slow realisation that civil war had begun.
See where Virus-bombing of Isstvan III occurred on the galactic map during the Horus Heresy.