Of all the great battles that wracked the Imperium during the Age of Darkness, few were as infamous as those fought in the Isstvan System.
First, on Isstvan III, Horus Lupercal launched his bloody betrayal with the systematic eradication of the loyalist elements of his co-conspirator Legions, dispatching carefully chosen waves of troops to the planet before wiping it clean with an apocalyptic virus bombardment.
The heroic acts of Death Guard Captain Nathaniel Garro alerted the Imperium to Horus’ treachery, and after much deliberation, a mighty Retribution Fleet was despatched to bring the Warmaster to justice. What transpired on Isstvan V is one of the darkest tragedies of the Horus Heresy, known forever after as the Dropsite Massacre.
This is its story.
The beginning: The Imperial Fists muster
Though he is initially hesitant to believe that the beloved and respected Primarch Horus has turned against the Imperium, Rogal Dorn sends out a call for all loyal sons of the Emperor to embark for the Isstvan System and bring the Warmaster to justice. His own fleets muster above Terra and leave to join the fight, but they are thrown off course by the tides of the Warp and left stranded in the Phall system – surviving only thanks to the ironclad command of Alexis Pollux.
The call is met by the Iron Hands, Salamanders, Raven Guard, Word Bearers, Night Lords, Alpha Legion and Iron Warriors, who all make their way Isstvan V. Some send tens of thousands of troops while others commit almost their entire strength, assembling one of the greatest concentrations of power in the Imperium’s history.
-399 hours Terran Sidereal: The retribution fleet arrives
The Raven Guard are among the first to arrive, immediately sending their stealthiest ships on reconnaissance missions that confirm the devastation wrought on Isstvan III by the Traitors. Ferrus Manus of the Iron Hands is not far behind, driven by a burning desire for vengeance against the Emperor’s Children for an earlier betrayal aboard his flagship. The Gorgon’s impressive record of compliance and mastery of war makes him the obvious choice of field commander for the loyalist forces.
Long-range scans reveal the bulk of the Warmaster’s forces are concentrated around a vast canyon known as the Urgall Depression, arrayed on the slopes of a towering peak surrounded by treacherous cliffs and boulder fields. A massive fortress rises above miles of defensive works, where thousands upon thousands of turncoat Space Marines wait for the oncoming assault.
-242 hours Terran Sidereal: Plans are formed, advice is ignored
As ships continue to arrive into the System and Imperial forces link up, strategists debate how to enact the Emperor’s judgement on Horus. It is clear the Warmaster has left nothing to chance, and though charging the might of the Legiones Astartes into the wolf’s jaws is seen as a brutish and wasteful manouever, it is nevertheless imperative that the traitors be brought to heel before their rebellion can spread.
Ignoring the prudence of Vulkan and guile of Corvus Corax, Ferrus Manus draws up a plan to crush Horus’ army with a single, overwhelming hammer blow. Though reckless, it is also one of the few plans with a chance of success – a fact his brother Primarchs begrudgingly accept.
-98 hours Terran Sidereal: Horus braces for impact
A network of spies spread across the Isstvan system relays word of loyalist preparations back to the Warmaster. His masterful defensive preparations have forced the loyalists into an attack on his strongest front, thanks to the impassable terrain and extensive void shield networks surrounding three sides of the Urgall Depression.
Vast batteries of Araknae and Tarantula sentry guns are placed behind fields of carefully placed mines, designed to funnel attackers through prepared killing fields. High above Isstvan V, orders are given and Space Marines board their transports – unaware of the horror they are about to carve into Imperial history.
Zero-hour Terran Sidereal: Battle is joined
The skies are lit by lance strikes from a dozen loyalist flagships in orbit, blasting the outer defences into smoking ruins and turning the black sand underfoot to glass. As the bombardment abates, drop pods run the gauntlet of the air defences and slam into the ground in their thousands, disgorging practiced waves of Space Marines who waste no time cutting through the Warmaster’s troops.
No quarter is asked for, nor is it given. One-time comrades butcher one another as the loyalists storm prepared defences and engage the traitors at point blank range from the outset. Ferrus Manus is among the first to meet the enemy, driving a murderous spearhead towards Horus’ distant fortress heedless of the losses incurred. Such a monumental cost was accepted before the first drop pod had left the Ferrum, and the Gorgon’s sons were all too ready to pay it.
Vulkan and Corvus Corax lead from the front in their own sectors, battling cohorts of savage World Eaters and sombre Death Guard as they push ever closer to their prize. Both Primarchs had marshalled almost the entire strength of their Legions for the assault, and for every warrior who falls, more are ready to drive the attack forwards.
There is little grace or martial artistry on display. Boltguns are fired until their ammunition runs dry. Chainblades are swung until their motors burn out. Veteran soldiers are reduced to desperate brawlers on the sand-choked plains, thrusting combat knives into vulnerable joints and swinging broken weapons like clubs – anything to grind one step closer to the Warmaster’s walls.
Despite it all, the Loyalists endure. Exhausted, they forge a ragged path through the maelstrom, knowing that at any moment reinforcements will arrive to join the attack and relieve their battered companies.
After four hours of bloody, pitiless slaughter, the next wave arrives.
+4 hours Terran Sidereal: The massacre begins
Traitor counter-attacks stall the Raven Guard and Salamanders amid great mounds of fallen bodies and burning tank wrecks, while the Iron Hands grind onwards girded by their burning desire for vengeance against the Emperor’s Children. The skies are lit once more by the burning trails of yet more landing craft, as four more Space Marine Legions – the Iron Warriors, Night Lords, Word Bearers and Alpha Legion – commit their forces to the battle at long last.
Ordered ranks of freshly armed troops march from their transports and quickly erect defensive fortifications, anchoring the back line of the loyalist advance with heavy gun emplacements and armoured vehicles. Battered companies disengage and fight their way back to the landing zones, their vox hails answered only by the quiet hum of static.
A red flare rises from the battlements of Horus’ fortress.
As one, the new arrivals raise their guns.
What had begun with hours of gruelling combat ends in moments. The reinforcing Legions cast off their masks and signal their allegiance to Horus by slaughtering every loyalist they can reach, firing ceaselessly into the press of bodies. It is the worst defeat suffered by Space Marines of any kind since their creation.
Far ahead, Fulgrim takes to the field and roars a challenge to Ferrus Manus, who responds in kind. Such is the carnage of their meeting that none survive who can say what exactly transpires, but after a titanic clash of world-shaking might, the lord of the Iron Hands lies decapitated at his brother’s feet.
Elsewhere, Angron and Mortarion rampage across the broken Loyalist lines. Horus finally emerges from the shadow of the infamous Titan Dies Irae to claim his final victory, claiming the severed head of Ferrus Manus and cutting down the last valiant Iron Hands who sought to protect it.
The Warmaster’s victory is absolute.
The aftermath: Horus begins his advance
More than nine tenths of the loyalist forces deployed to the surface of Isstvan V are lost to the Dropsite Massacre. In the wake of the betrayal, Corvus Corax meets Lorgar in single combat and nearly kills the master of the Word Bearers before Konrad Curze intervenes and saves his brother. Vulkan is last seen in a plume of atomic fire that kills his remaining sons, fighting to the last under a cataclysmic barrage of Iron Warriors firepower.
Those few loyalist survivors who scatter into the wastes or make it off-world are forever haunted. Many coalesce into ad-hoc warbands known as the Shattered Legions. Now there is no doubt that Horus and his Traitor Legions have launched a full-scale rebellion against the Emperor, plunging the galaxy into an Age of Darkness that will drown the shining glories of the Great Crusade in blood and chaos.
You can fight through the dark hours of the Dropsite Massacre yourself using the upcoming Saturnine boxed set for the latest edition of Warhammer: The Horus Heresy – Age of Darkness, which is out soon.
