|None, was 12 billion pre-Heresy
Isstvan III was a Hive World in the Isstvan system. Its destruction and the surrounding circumstances were the first overt signs of Warmaster Horus's turn to the forces of Chaos and the first battle of the Horus Heresy.
Having been founded sometime during the Dark Age of Technology and spared many of the horrors of the Age of Strife, Isstvan III was originally assimilated into the Imperium by the Raven Guard during the Great Crusade. The Raven Guard swiftly conquered the planet, attacking from orbit at night and destroying most of its limited military capabilities in one swoop. By the time dawn rose on the Hive of Khry Vanak, Isstvan III's capital, the planetary leadership and military capability had been bombed into ruin. Aftewards, the administration of the Imperium moved in the wake of the Astartes and rebuilt the planet along the lines of the Imperial Truth.[5a]
Rebellion and Heresy
Baron Vardus Praal, Imperial governor of the Isstvan system, eventually rose in revolt against the Imperium, purging Imperial elements for as long as six years before word of the rebellion reached the Council of Terra.[5b] The Emperor of Mankind and the Council, ignorant of the change in Horus, charged the Warmaster with crushing this rebellion. Under his command were four Space Marine Legions; his own Sons of Horus, the Emperor's Children of Fulgrim, Mortarion and his Death Guard, and the World Eaters led by Angron. Horus and these Primarchs had fallen to Chaos and took this opportunity to purge all suspected loyalists from their Legions.
The planned first wave, all suspected loyalists, deployed by Drop pods upon the Choral City, the capital of the planet. Not using the traditional Stormbirds and cutting their communication lines to the fleet, Horus tried to ensure that none of them would survive the massive virus bombardment. Captain Saul Tarvitz of the Emperor's Children, working on a hunch, had managed to remain in the fleet, where he discovered the planned bombardment and commandeered a Thunderhawk to save his betrayed brethren. Thanks to Tarvitz's warning, a few hundred loyal Space Marines managed to survive inside airtight bunkers and bomb shelters. As the putrid gases resulting from the rapidly decaying organic matter filled the atmosphere, Horus ignited a firestorm on the planet which melted the hives and razed the cities. The psychic death scream of the twelve billion is said to have been louder than the Astronomican.
Despite this, many loyalists of the four Legions managed to survive, and an enraged Angron, acting against Horus's orders, led his Legion to the surface to slaughter the survivors. Horus, trying to salvage the situation, sent detachments of all his Legions to slay the Loyalists. The Loyalists, fighting tenaciously, turned the planned slaughter into a full-scale battle. Under the command of Captains Garviel Loken and Tarik Torgaddon of the Sons of Horus (redubbed the Luna Wolves), Saul Tarvitz of the Emperor's Children, and Ehrlen of the World Eaters, the loyalists were able to mount a surprising defence in the ruins of the capital city. Ultimately, the Loyalists were crushed, in part to Lucius's betrayal and the orbital bombardment of the Choral City, but made Horus pay dearly. The battle lasted for three months and inflicted huge losses upon the traitors. It was a Pyrrhic victory at best. While the battle raged upon the planet, a handful of loyalists led by Captain Nathaniel Garro of the Death Guard managed to commandeer the frigate Eisenstein and fled to warn the Emperor of Horus's betrayal.
Isstvan III would remain a barren, quarantined world. However, 10,000 years later the sole survivor of the original atrocity, the Dreadnought Rylanor, enacted his revenge. Using a sonic beacon to draw Fulgrim to the world, Rylanor detonated an unexploded Virus Bomb. Once again Isstvan III was scoured of whatever life had redeveloped over the millennia, but Fulgrim managed to survive.
The system and planet's name is alternatively spelled Istvaan.
- 1: Galaxy in Flames (Novel), [Needs Citation]
- 2: Realm of Chaos: Slaves to Darkness, pg. 240
- 3: Codex: Chaos Space Marines (3rd Edition, 2nd Codex), pg. 5
- 4: Fallen Angels (Novel), [Needs Citation]
- 5: The Horus Heresy Book One - Betrayal
- 6: The Ancient Awaits (Short Story) - Sons of the Emperor (Anthology)