The Great Crusade

When the Warp storms that had cut off Terra subsided, and the Age of Strife came to an end, the Emperor deemed it time to begin his Great Crusade, a massive galactic campaign by which he and his armies would free human worlds from oppression and unite the human race across the galaxy under a single banner once again. Much of this can be read elsewhere: suffice to say that to execute this grand plan the Emperor conceived of the Primarchs, his god-like, genetically engineered superhuman offspring. The Primarchs were still in their infancy, however, when they were snatched away from the special laboratory beneath the Imperial Palace where they had been developed. Debate still rages about the cause of this; some argue that the Emperor sent the Primarchs away so that they could learn in their own way, others argue that the Chaos Gods broke into the Palace and, unable to destroy them completely, scattered the Primarchs throughout the Warp, where they eventually came to rest on diverse, human-inhabited worlds.

During the Great Crusade, the Emperor encountered each of the Primarchs in turn. A Space Marine Legion had been created from each of the Primarchs' genetic material, and so the Emperor, unable to be everywhere at once, deemed it fitting that each Primarch should lead their offspring. However, this would prove a critical mistake, for after some time many in the Legions would come to venerate their Primarch more than the Emperor.

After 200 years of hard conflict in the thirty-first millennium, over two million worlds had been reclaimed by the Emperor in the name of humanity. Beside him stood Horus, who had fought beside the Emperor for the early part of the Great Crusade as his only rediscovered son. The long wars had forged a strong bond between them, and they were truly like father and son. But now the Emperor had to consolidate his new empire, and more importantly undertake the next phase of his Grand Plan. This required his own presence on Terra, and so after Horus' magnificent victory in the Ullanor Crusade against the largest horde of Orks ever encountered to that time, the Emperor asked Horus to change the name of his Legion from the Luna Wolves to the Sons of Horus. Never before had such an honour been bestowed, though Horus initially declined and only relented a few years later after a tragic encounter with the independent human-led Interex confederacy. The Emperor also proclaimed Horus the Warmaster, the ultimate leader of all the Imperium's armies, and declared that he would lead the other Primarchs and their Legions through the remainder of the Great Crusade.

At this announcement there was much shock and outrage. Many of the other Primarchs didn't understand why the Emperor was leaving them, and worse still why Horus should have command over them. Some, like Sanguinius and Fulgrim, were pleased for their new Warmaster, while others, like Angron and Perturabo, were furious at Horus's new appointment. Adding fuel to Perturabo's rage was the redeployment of his rival Rogal Dorn and the Imperial Fists Legion to Terra to serve as the Emperor's Praetorian Guard.

The Corruption of the Legions

During the Great Crusade, it became apparent that the Primarchs were far from the perfect beings they were designed to be. Although each Primarch was physically and mentally godlike, their personalities were each as flawed as those of any mortal. During their upbringing on their respective homeworlds, the Primarchs had to learn humanity from mere humans; for almost all of the Primarchs, this resulted in their harbouring all-too-human flaws (for specific examples, see each Legion's history).

Horus took over command of the Great Crusade, and took up his new duties with earnest dedication. However there was much dissension in the ranks of the Primarchs and other parties. Only a handful of the Primarchs, among them a scheming Lorgar, remained steadfast beside him during this period of dissension. Horus also disagreed with many of the Emperor's new decrees intended to shift the burden of taxation and administration onto the newly-conquered ('compliant') worlds. Even worse, Horus came to believe that he was failing his father, and was deeply wounded that the Emperor had revealed to none of the Primarchs, not even his favoured son, why he had secluded himself upon Terra. These seeds of bitterness, resentment and frustration grew, and would soon bear deadly fruit...

Meanwhile, the Emperor was on Terra organising the infrastructure for his Imperium to function. He created the Council of Terra, a body of bureaucrats and nobles that would implement and administer the new galaxy-wide tax called the Imperial Tithe and other matters of day-to-day law in the Imperium of Man.

The news of the creation of the Council of Terra and its latest bureaucratic edicts angered some of the Primarchs still further. They did not understand why they, the Emperor's greatest champions, who had spilled their blood on a thousand worlds to re-unify all the races of Man, did not have seats on this new Imperial ruling body. The brotherhood of the Primarchs was being shattered bit by bit by this growing resentment and jealousy. Old arguments and differences came to the fore. Horus became ever more distant from the Emperor, seeking only glory for himself and his Legion.

It was on the moon of the world of Davin that Horus's fate was sealed. This was the second time his Legion had been posted to this world; after the previous visit sixty years earlier the Luna Wolves had adopted the native Davinite institution of warrior lodges. Though these lodges had begun as simple fraternities of warriors, their secretive nature handed Lorgar, the Primarch of the Word Bearers Legion, and his First Chaplain Erebus, the tool they needed to manipulate Horus. Lorgar and his Word Bearers came from a world of religious fanaticism, and had long worshipped the Emperor as a living god. The Word Bearers had sought to spread this Cult of the Emperor to every world they added to the Imperium; but the Emperor hated organized religion, blaming it for much of the darkness that had plagued humanity's history. The Emperor forbade any religious worship in his empire, preferring that his subjects instead accept 'Imperial Truth'-- that reason and science alone presented the tools with which to create a better human future.

Lorgar did not suffer the Emperor's harsh reprimand well. Angered that the Emperor would not accept his devotion, Lorgar turned instead to the Ruinous Powers of the Warp - who were all too willing to accept the devotion of one of humanity's Primarchs. Before long the Word Bearers Legion had been almost entirely corrupted by the Chaos Gods, and Lorgar and his First Chaplain were tasked by the Chaos Gods with corrupting all of their fellow Space Marines--starting with the greatest of them all, the Warmaster Horus.

On Davin's moon, which had been corrupted by the forces of the Chaos God Nurgle, Horus was poisoned by a Chaos-tainted blade wielded by the Chaos-corrupted form of the Imperial Army commander the Warmaster had left behind to govern Davin sixty years before. The potent Chaos sorcery of the blade left Horus with a bleeding wound in his shoulder that his legion's apothecaries could not heal, despite the Primarch's superhuman immune system and their own advanced medical technology. Seeing his chance to further the designs of Chaos, Erebus persuaded the Sons of Horus's warrior lodge to allow a group of Davinite shamans - Chaos cultists all - to heal him.

During the rituals, Horus's spirit was transferred into the Warp. There, he bore witness to a terrible vision of the future (which his actions would bring about) - the Imperium as a repressive, violent theocracy, where the Emperor and his Primarchs (but not Horus) were worshipped as divine beings by the masses. The Chaos Gods portrayed themselves as victims of the Emperor's psychic might, and who had no interest in the material world. Horus, already having grown jealous and deeply resentful of his perceived poor treatment at the hands of the Emperor, proved all too willing to accept the Ruinous Powers' false visions. Horus decided that if anyone deserved such an accolade it was he, and not the Emperor, who deserved to be worshipped as a god. The Chaos Gods' pact with Horus was simple: "Give us the Emperor and we will give you the galaxy". He accepted the offer of the Chaos Gods to join their cause: they healed his grievous wound and also gave him access to the powers of the Warp.

Renouncing his oath to the Emperor, Horus led his Legion into worship of the myriad Chaos Gods. He then sought to turn many of his fellow Primarchs to Chaos, and succeeded with Angron of the World Eaters, Fulgrim of the Emperor's Children and Mortarion of the Death Guard, who were first of many to follow, along with many regiments of the Imperial Army and several Titan Legions.

Magnus the Red, Primarch of the Thousand Sons Legion, foresaw Horus's actions through his Legion's own use of forbidden psychic sorcery. Magnus then attempted to forewarn the Emperor of the impending betrayal. However, knowing that he would have to find a means of quickly warning the Emperor, and as an act of both desperation and vindication, Magnus used sorcery to send his message to the Emperor. The message penetrated the psychic defences of the Imperial Palace on Terra, shattering all the psychic wards the Emperor had placed on the Palace - including those within his secret project in the Imperial Dungeons: the creation of a warp-gate to invade the Eldar's Webway. Refusing to believe that Horus, his most beloved and trusted son would betray him, the Emperor instead perceived the traitor to the Imperium to be Magnus and his Thousand Sons Legion. The Emperor ordered the Primarch Leman Russ to mobilize his Space Wolves Legion and take Magnus into custody; however Horus convinced Russ that Magnus was a traitor and needed to be destroyed.

The Istvaan Incidents

Published materials are inconsistent on their spelling of "Isstvan": the more recently published material uses "Isstvan",^[1] while other (generally older) materials use "Istvaan".^[2][3] No explanation for this difference has been provided.

Preparations and Allegiances

Much of Horus's success arose from the thorough groundwork he had laid before the opening shots were fired at Istvaan. He had already swayed Angron and Mortarion. Lorgar, who had been responsible for the budding rebellion, was also with Horus. Three of the most loyal Legions, the Dark Angels, Blood Angels and Ultramarines and their Primarchs, were sent on missions far from Terra and Istvaan. The Imperial Fists and White Scars were too close to Terra to be contacted without raising suspicion, though Horus believed - mistakenly - that Jaghatai Khan would ultimately take his side. Shortly before the Dropsite Massacre, Fulgrim also attempted to sway Ferrus Manus to Horus's cause, failed, and barely escaped with his life. Fulgrim promised he would deliver Manus's severed head to Horus in recompense. The Blood Angels were sent to the daemon-infested Signis Cluster and the Ultramarines to Calth, where a large Word Bearer force, under Kor Phaeron, had massed.

Of the other eventual traitors, Night Haunter was due to face disciplinary action from the Emperor; Alpharius had always been closer to Horus; and Perturabo's bitterness towards Rogal Dorn made him an easy target for corruption. The Thousand Sons had never planned to join Horus, but when betrayed by the Emperor and the trap Tzeentch had laid for the Red Sorcerer's legion led them to his side regardless.

The remaining Legions - the Raven Guard, Salamanders, Iron Hands and Space Wolves - remained staunchly loyal to the Emperor, though all but the Wolves would pay dearly for it in the battles to come. Beyond the Legions, Horus had already swayed Adept Regulus with promises of the STCs recovered during the war with the Technocratic Brotherhood, delivering Mechanicus support to the Warmaster's forces.

Istvaan III

The first sign that Horus and his Legion had turned to Chaos was made evident when Horus virus bombed the rebel world of Istvaan III. The Planetary Governor of Istvaan III had declared his independence from the Imperium, and the Council of Terra charged Horus with the retaking of that world. This order merely furthered Horus's plans. Although the four Legions under his direct command had turned Traitor, there were still some Loyalist elements within the Sons of Horus, World Eaters, and Death Guard; many of these were Terran Space Marines who had been recruited before being reunited with their Primarchs. Horus, under the guise of his orders, amassed his troops in the Istvaan System.

Horus had a plan by which he would destroy all Loyalist elements of the Legions at his command. After a lengthy bombardment, Horus despatched all Loyalist Marines down to the planet, with the pretense of bringing it back into the Imperium. At the moment of victory, however, these Marines were betrayed when virus bombs began to rain down on the planet. However, some Marines loyal to the Emperor had remained onboard their ships, and as Istvaan III died, these soldiers fought desperately to warn their brethren on the surface. Their sacrifice saved many Space Marines, as they were able to take shelter before the virus bombs struck. The population of Istvaan III received no such protection. Sixteen billion people died almost immediately. The psychic shock of so many simultaneous deaths shrieked through the Warp. A contingent of Loyalists led by Captain Garro of the Death Guard escaped the fleet orbiting Istvaan III aboard the damaged vessel called Eisenstein, and fled to Terra to warn the Emperor.

Angron, realising that the virus bombs had not been fully effective against the Loyalist Marines, flew into a rage and hurled himself at the planet with 50 companies of Marines. Horus was furious at Angron for delaying his plans, yet reluctantly reinforced him with troops from the Sons of Horus, the Death Guard, and the Emperor's Children. On Istvaan III, the remaining Loyalists, under the command of Saul Tarvitz, fought bravely against their own traitorous battle-brothers. But their cause was doomed. Soon only a few hundred of them remained until, finally, Horus grew unable to tolerate the delay and forced Angron to withdraw his forces, and ordered a systematic orbital bombardment that killed Istvaan III's last brave survivors.

Flight of the Eisenstein

The seventy Loyalists led by Captain Garro commandeered the Imperial frigate Eisenstein and, evading the forces of Horus, were able to escape from the Istvaan System into the Immaterium. The Eisenstein was badly damaged during its escape from Istvaan III; all its astropaths were dead, and its lone Navigator was mortally wounded. However, Garro managed to attract the attention of passing Loyalist ships by setting the vessel's Warp engines to self-destruct and ejecting them from the ship. Rogal Dorn's Imperial Fists Legion had been becalmed in the Warp with its fleet for some time, and his Navigators sensed the detonation of the Eisenstein's Warp drives. Making an immediate course for the location of the ship's beacon, Dorn met with Garro, who explained to him all that had happened with the Traitor Legions.

The Eisenstein was able to reach Terra, allowing the loyal Marines to report the extent of the atrocities that had occurred in the Istvaan System. It was said in later millennia that without this warning, the Imperium would have faced even greater difficulties responding to Horus's final moves.

The fate of these seventy Marines is ultimately unknown. Some believe they continued to fight for the Emperor until death claimed them, while others maintain that they were treated as if they were their traitorous brethren, either imprisoned and left to rot, or executed. Others believe that Captain Garro, shocked by the terrible betrayal, became an Apothecary, vowing never to kill again.

Yet there is another story concerning their fate. Malcador the Sigilite had presented eight of the survivors to the Emperor before his departure. These men were gifted psykers, came from the ranks of the Legions that had turned Traitor, and yet maintained both an unbreakable faith in the Emperor and talent for resisting the temptations of Chaos. Many believe these men formed the nucleus of the elite Space Marine Chapter known as the Grey Knights.

The Drop Site Massacre In response to Horus's betrayal, Rogal Dorn ordered seven Space Marine Legions to Horus's base on the world of Isstvan V to challenge the Warmaster. These Legions were the Iron Hands, Salamanders, Raven Guard, Night Lords, Alpha Legion, Iron Warriors, and Word Bearers. Of these, the Night Lords, Alpha Legion, Iron Warriors and Word Bearers had all turned to Chaos.

The three Loyalist Legions, the Iron Hands, Salamanders and Raven Guard, were deployed in the first wave, and attacked the Traitor Marines' forces. As they gained a foothold on the planet, at a heavy cost, Ferrus Manus's obsession with confronting Fulgrim came to the fore and he abandoned his post as Supreme Commander. As the two dueled, Horus committed his hidden reserves, swamping the beleaguered attackers. They fell back towards the drop zone the other four Legions had established, only to be fired on by their 'allies'.

Each Loyalist Legion was almost destroyed in the resulting bloodbath, recorded in Imperial history as the Drop Site Massacre. Ferrus Manus was slain by Fulgrim as all around him were massacred. Some believe Alpharius, Primarch of the Alpha Legion, planned the operation jointly with Horus. Of the three Legions loyal to the Emperor on Istvaan V, only a handful of survivors escaped, including a critically wounded Primarch Corax of the Raven Guard. The Drop Site Massacre is also the last known place where the Primarch Vulkan of the Salamanders Legion was seen.

(Note: Vulkan was heard from after the end of the Heresy, as, like Russ and Dorn, he is recorded as having objected to the Second Founding. This event is supported by Index Astartes: Black Templars and the Black Templar Codex. The fate of Vulkan is unknown, so some assume the piece concerning the discussion about the Codex Astartes was a mistake in the lore or a suggestion of Vulkan's ideals after his death (as parts of the the Codex Astartes was written prior to the Heresy. However, since Index Astartes: Salamanders doesn't mention more, Vulkan's fate remains unknown.)

The Route to Terra

After the Drop Site Massacre, it became clear that eight of the eighteen Legions had turned to Chaos. Horus openly declared that he would no longer follow the Emperor, believing him to be undeserving of the battles fought in his name, and took leadership of the Traitor Legions, supported by elements of the Imperial Army, a large portion of the Adeptus Mechanicus, the Imperial Navy and the daemon-spawn of Chaos. Their aim soon became clear: Terra, the heart of the Imperium.

Rogal Dorn and Malcador the Sigilite, receiving the few survivors from the Dropsite Massacre, became aware of the full implications of their position. Only the Imperial Fists and Imperial Army defended Terra, and those loyal to the Emperor elsewhere were cut off and weakened. He immediately recalled all Imperial forces back to Terra in preparation for Horus's invasion.

The Sons of Horus, the Death Guard, the Emperor's Children, the World Eaters, and elements of the Word Bearers, prepared to rendezvous at Mars. The rest of the Word Bearers Legion was winning the Battle of Calth, and the Blood Angels were still embattled on Signis. The majority of the Imperial Fists' fleet was trapped in an area of the Warp becalmed by the Chaos Gods. Horus assigned the Primarch Perturabo of the Iron Warriors to engage this large force of the Imperial Fists and cripple their fleet.

At this time the Space Wolves had completed the Burning of Prospero, near the Chondax System, where the White Scars Legion was stationed. The Dark Angels were engaged in an unknown campaign on the Eastern Fringe of the galaxy. Suddenly the Alpha Legion's fleet broke from the Warp to engage the Space Wolves forces of the Primarch Leman Russ, hammering his smaller force and forcing Russ to resort to hit and run attacks. The Alpha Legion's Primarch Alpharius also attacked the nearby White Scars piecemeal in order to draw that larger, newly-reinforced Legion into the conflict, and keep them from jumping to Terra to aid in its defense.

The Primarch Jaghatai Khan desperately wished to send his White Scars Legion to aid Russ. And yet as the Traitor Legions' ships attacked, Khan received the order from the Imperial Fists' Primarch Rogal Dorn: return to Terra immediately and regardless of all other considerations. Dorn also ordered Khan to relay the order on to Leman Russ and the Space Wolves, and to add that, should Russ succeed in evading his Alpha Legion attackers, only then should he attempt the Warp jump to Terra. Relaying the message and adding his apology, the Khan and his Legion made the jump to Terra. Leman Russ shrugged, and prepared to meet the Alpha Legion with renewed determination. (With help from an unlikely quarter, the Space Wolves would eventually turn the tables on their attackers and make the Warp jump to Terra.)

As this happened, the Night Lords arrived in the Eastern Fringe of the galaxy to engage the Dark Angels, and Perturabo's armada broke Warp to engage the Imperial Fists' fleet marooned near the Chaos Space Marines' headquarters world of Istvaan V. Surviving the initial thrust of the Iron Warriors' attacks, the Fists' armada held fast and scattered Perturabo's fleet, before Rogal Dorn had his ships make their own Warp jump to Terra.

Meanwhile, in the Signis Cluster, the Blood Angels, granted new and terrible power by a mysterious mass rage (that would resurface again during the Siege of Terra) had triumphed, smashed the Chaos daemon horde they faced asunder before making the Warp jump to Terra.

Similarly at the world of Calth, the Primarch Roboute Guilliman's battered Ultramarines expeditionary force had dug in on the surface, while Roboute himself and the remnants of the Ultramarines' fleet in space began to organise hit-and-run attacks on the lumbering Word Bearers. Surveying the scene on the planet, Guilliman rapidly assessed his ground troop's positions, and began broadcasting clear, concise orders to his men, co-ordinating each pocket of defence. One such pocket, under Brother-Captain Ventanus, organised a breakout and retook Calth's defence lasguns. Ventanus's victory served to even the odds in space, buying time for the vast remainder of the Ultramarines Legion to arrive at Calth and drive off the Traitors. Now reunited, the Ultramarines finally received Malcador's orders, and immediately made the Warp jump to Terra.

As the Warmaster was moving for Terra he received an unexpected communication from the recently betrayed Thousand Sons Primarch Magnus the Red. The Space Wolves had driven the Thousand Sons from Prospero. Magnus pledged his allegiance and the allegiance of the Thousand Sons Legion to Horus and the Chaos Gods in retaliation against the Emperor for this betrayal. The Thousand Sons were en route to Terra where they would link up with Horus's forces. Of the nine remaining Loyalist Space Marines Legions, only the White Scars and Blood Angels were able to join Rogal Dorn and his Imperial Fists in the defense of Terra. Three entire Titan Legions and close to two million soldiers of the Imperial Army stood alongside them.

The Siege of the Imperial Palace

The Landing on Terra

The siege began with an orbital bombardment by the forces of the Warmaster, designed to weaken the defences of the Emperor's Palace and prepare a full scale invasion of the planet. Although the Loyalist fleets and defences fought back, they, like the soldiers on the surface, were too few, and soon were ground down without mercy.

After days of bombardment, the Traitor Space Marines landed on the surface in drop pods, ready to take the two spaceports nearest the Imperial Palace. Five Traitor Legions participated in the drop, combining with Traitor forces on the surface. The Eternity Wall and the Lion's Gate Spaceports fell to the Chaos Marines in hours. Dark Chaos cultists made their invocations, calling down the Greater Daemons of Chaos onto Terran soil from the Warp.

The spaceports secured, Horus's troops landed en masse, and the hulking transports carried thousands of men each. The transports' immense size made them prime targets for Terra's defence lasers. Although many landing ships were destroyed, many more landed on the surface, disgorging yet more soldiers, Imperial Army armour and Titans to augment the besiegers' strength. They met stiff resistance, the Imperial defenders knowing that the survival of their homeworld, their Emperor, and the entirety of the human race depended on their resolve.

The Siege

The besiegers forced the defenders back to the very walls of the Imperial Palace, where the assault slowed. Around the walls of the Imperial Palace men died in their thousands, clearing enemy troops from the walls only to find twice as many charging forwards.

The defenders' resolve was tested sorely as they beheld their enemy. Daemons, superhuman Chaos Space Marines, and Traitor Imperial Army; all men who had once been their greatest allies. In the besiegers, the defenders beheld a twisted mirror vision of themselves, seeing the darkest, corrupted traits of humanity staring back at them, a foreshadowing of what would befall the Imperium if Chaos triumphed over the Emperor.

Angron, now a daemon prince, came forth and demanded that the Loyalists surrender. They were cut off, he said, outnumbered, and defending a ruler unworthy of their loyalty. It was the beginning of the darkest days for the defenders; many would have given up then were it not for the presence of the angel Primarch Sanguinius, winged leader of the Blood Angels. The two Primarchs gazed at each other, possibly communicating by telepathy. Eventually Angron withdrew, telling his forces that there would be no surrender.

The siege began again, in earnest. Each Imperial defender knew he was already dead, that it was only a matter of how many Traitors would go to their graves alongside them. Three times the hordes of Chaos scaled the walls, and three times they were beaten off with savage tenacity by Sanguinius and his Blood Angels. Outside the walls, the defenders led by Jaghatai Khan tried to draw the main body of the besieger's army away from the Palace, each time meeting with failure. Soon the outnumbered defenders were pushed back into the maze of corridors and bulwarks within the Palace's very walls. Frustrated with his army's slow progress, Horus ordered the Fire Wasps Traitor Titan Legion to demolish entire sections of the wall. Despite grievous losses, the Titans gouged open great breaches in the wall. The Traitors surged into the Palace, killing with renewed fanaticism.

Meanwhile, Jaghatai Khan decided on a change of plan. Rather than assaulting the nigh-invincible bulk of the besiegers' army, Khan redirected his White Scars Legion and the surviving Loyalist Imperial Army Tank Divisions to Lion's Gate Spaceport. The Khan's lightning raid struck at dawn, and surprised the Traitors completely. The spaceport was retaken. Khan ordered his troops to create a perimeter around the port and to reactivate the defense laser batteries. These began firing on Horus's unprotected dropships, as Khan's troops repelled a series of frenzied counter-attacks from the besiegers. Khan's plan had worked: the flow of men and machines to the Palace had been halved at a single stroke. An attempt to reseize the Eternity Wall Spaceport inspired by this success was in vain.

At the Palace, the retreating defenders had been forced back to the Eternity Gate, the sole point of entry into the Imperial Palace. The Blood Angels and Imperial Fists defied hordes of Chaos troops, while the remaining Imperial Army troops fell back through the Gate. Then the mighty Bloodthirster Ka'bandah came forth, and bellowed out a challenge to Sanguinius. The Angel would never have time to answer. The daemon hurled itself at Sanguinius, barely allowing him time to parry the daemon's strikes. All fell silent. Daemon and Angel took to the sky. Fatigued from the siege, Sanguinius lost the upper hand and was cast down by the daemon, pulverising the concrete below upon impact. The invaders roared with triumph. The defenders wailed in despair.

Yet the Blood Angels' Primarch was not beaten. He had made a promise to the daemon on the Signis Cluster. Now was the time to fulfill it. Sanguinius forced himself back to his feet and took to the sky. Flying as swift as a missile, the Angel took the daemon by surprise. He seized the daemon's ankle and right arm. A burning corona of light playing about his head, now terrible in aspect, Sanguinius hefted the creature high, and snapped its back over his knee like a twig. Sanguinius hurled the carcass back at the horde which howled in frustration and dismay, as the Eternity Gate slammed shut.

The Endgame

The Emperor and Horus in the endgame of the Heresy, with the Primarch Sanquinius lying dead at Horus's feet.The siege lasted 55 days. Both sides knew the defeat of the Imperium was near. Sensing this, Horus prepared to teleport to the surface to lead his forces in person. Before this could happen, the Word Bearers' First Chaplain Erebus broke the news to Horus: Their daemonic allies had told him that the Ultramarines and Space Wolves Legions were nearing Terra; only a short distance behind them were the Dark Angels Legion. While Erebrus knew the other two legions would arrive in mere hours, he could not be precise about the exact time of Jonson's arrival.

At that moment, Horus realised that his gamble had failed. Weeks of further conflict would be needed to break the defenders; the Emperor's reinforcements would arrive in mere hours. It was then that Horus gave the most fateful order of the entire Heresy. He ordered his flagship Vengeful Spirit's shields dropped, immediately. By so doing, Horus hoped to draw the Emperor from the surface and force him into a duel.

The Emperor rose to the challenge, leading his Adeptus Custodes, the Primarch Sanguinius, Rogal Dorn and several Imperial Fist and Blood Angel Space Marines in Terminator armour in the assault. Horus used his powers to scatter the Emperor's force throughout the massive warship. Each fought a series of battles aboard the corrupted ship, attempting to link up with their comrades and confront the Warmaster. It was Sanguinius who reached Horus first. The Warmaster attempted to lure the Blood Angel Primarch to his side; when Sanguinius refused, Horus attacked. Sanguinius, wounded from his battles on Terra, was no match for Horus, now at the height of his daemonic power, power almost enough to rival the Emperor. Horus strangled the Angel with contemptous ease.

Then the Emperor entered. He saw the corpse of Sanguinius, lying at Horus's feet. Horus told the Emperor he was a fool for refusing the power that the Chaos Gods offered; power that he had used to tame them to his will. If the Emperor would kneel before him, Horus would spare his life. The Emperor knew well the trap that had snared his son. No one could master Chaos, the Emperor replied, Chaos itself was always the master of those it seduced: Horus had deluded himself. Horus was the servant, not the master. Snarling, Horus sent bolts of lightning at the Emperor. The Emperor nullified them. The die was cast: Each god-like being knew the fate of humanity hung in the balance.

The Emperor and Horus engaged one another, battling physically and psychically. Though the Emperor's psychic gifts and martial skills were unmatchable, he found himself unwilling to summon his full power against his first son. He suffered grievous wounds at his fallen son's hands. After a score of thrusts, parries and counter-thrusts, Horus opened the Emperor's jugular and severed the tendons in his right wrist. A psychic blast seared the flesh from the Emperor's face, bursting an eye. Horus tore the Emperor's right arm from its socket, and broke his back over his knee.

At that moment, a lone Adeptus Custodes warrior entered the bridge. Horus showed him the Emperor's broken form and laughed mockingly at the Custode. He roared and charged the Warmaster immediately, only to be incinerated in an instant by a psychic blast from Horus. (In previous editions of the tale, an Imperial Fist Terminator attacked Horus; in older versions, the deed is ascribed to an Imperial Guardsman named Ollanious Pious.)

The casual brutality of the act galvanised the Emperor. Realising at last that his favoured son was truly lost to the corruption of Chaos, the Emperor finally mustered his full power, and unleashed a lance of pure Warp energy that pierced the gloating Horus's defenses. So powerful was the attack that the Chaos Gods themselves recoiled in terror, withdrawing rapidly from their mortal pawn, for fear that the Emperor would kill them too. Just before Horus died, he looked his father in the eye, shedding a single tear. The Emperor saw regret in his fallen son's eyes. He also knew Chaos could attempt to possess Horus once more, and that he would not be there to halt him a second time. Driving all compassion from his mind, the Emperor obliterated Horus from the mortal plane.

The Warmaster's death sent a psychic shockwave surging across the Solar System, casting the Chaos daemons back into the Warp, spreading mass panic in seconds. It became clear to the forces of Chaos that their leader had been defeated. A berserker fury encompassed the Blood Angels at the moment of their Primarch's death, and they surged forth to scatter the attackers. Retreat turned to rout, and rout turned to bloodbath; scores upon scores upon scores of Traitor Marines and Titans fell as they attempted to flee.

Meanwhile, Rogal Dorn finally found his way to the ship's bridge, only to discover his fallen brother, Sanguinus, and the Emperor, on the verge of death. It was then that the Emperor whispered instructions to Dorn, urging the Imperial Fists Primarch to take him to the Golden Throne. The surviving Loyalists teleported back to the Imperial Dungeons. Here Malcador the Sigilite, who had briefly taken the Emperor's place on the Throne, thus keeping the warp-gate beyond it closed, collapsed to dust as he was removed and the Emperor put in his place. The Emperor spoke his final words to his followers, urging them to continue the fight to free humanity from the forces of Chaos and ignorance that continued to assail it. And then the master of mankind spoke no more, his body entombed within the life support mechanisms of the Golden Throne, his spirit trapped in a crippled and mortally wounded body for millennia to come. The Imperium of Man survived, but it would become the bastion of repression, superstition and brutality that the Emperor had fought against. It also would offer humanity the only chance for survival in an increasingly hostile universe.

The Aftermath

As the flames of the civil war subsided, Ultramarines Primarch Roboute Guilliman rallied the surviving Loyalists, stretching his Legion thin across the galaxy in a bid to buy precious time for the others to rebuild and rearm. While some Chaos Legions fled to the safety of the vast Warp storm known as the Eye of Terror, the Iron Warriors held fast on the worlds they had conquered and were dislodged only after decades of gruelling warfare. As the Scouring (the name given to the Loyalists' campaign to drive the Traitor Legions from Imperial space) was initiated, the Night Lords Legion continued their spree of genocide and terror along the Eastern Fringe of the galaxy. This campaign endured until the Night Lords' Primarch Night Haunter, suddenly perceiving himself as the embodiment of the very tyranny and brutality he had once fought to prevent, allowed a Callidus assassin to kill him on the world of Tsagualsa. The Alpha Legion's Primarch Alpharius lured the Ultramarines into a trap on the world of Eskrador, where he was slain by his hated nemesis, the Ultramarines' Primarch Roboute Guilliman. Yet Alpharius' subordinates, trained for independent command, denied the Ultramarines a complete victory, and managed to trap the older Legion and force heavy casualties upon their army. In the end the Ultramarines quit the field, opting to bombard the Traitor Marines from orbit.

As the last of the Traitor Legions fled into the great Warp storm known as the Eye of Terror at the end of the Scouring, the Ultramarines' Primarch Guilliman at last turned his attention to restructuring the Imperium. Never again should it succumb to a Heresy so vast. Significant Imperial organisations to be formed in response to the Horus Heresy were the Imperial Navy and Imperial Guard, who before had been joined together as the unified Imperial Army. The Inquisition became much more prominent after this time (some sources suggest that it was formed even before the Horus Heresy by the Emperor), and the Grey Knights Space Marines Chapter was formed to combat future daemonic incursions onto the material plane. The Council of Terra was succeeded by the High Lords of Terra: the 12 most powerful individuals in the Imperium, representing each of the various arms of the Imperial government and society and serving as the collective regency of the Imperium while the Emperor remained incapacitated. But of all the changes brought upon the Imperium of Man by Roboute Gulliman after the Horus Heresy, the most pivotal was the Second Founding, which saw the remaining Loyalist Space Marine Legions broken up into smaller, more flexible 1000-man units known as Chapters. Though the Primarchs Rogal Dorn, Vulkan and Leman Russ opposed this measure, Guilliman had the backing of the Primarchs Corax and Jaghatai Khan and the High Lords of Terra, and the measure passed. Never again would one man wield the incredible power of an entire Space Marine Legion.