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Horus Heresy

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Horus Heresy
Horus vs The Emperor.jpg
The Emperor confronts Horus aboard the Vengeful Spirit
Date 005.M31[7] — 014.M31[12]
Location Imperium
Battles Battles of the Horus Heresy
Outcome Pyrrhic Loyalist victory
Emperor interred to the Golden Throne[2e]
Beginning of the Great Scouring[20]
Loyalists Traitors
Emperor of Mankind (WIA)
IF Icon.png Rogal Dorn
DA Icon.png Lion El'Jonson
WS Icon.png Jaghatai Khan
SW Icon.png Leman Russ
BA Icon.png Sanguinius
IH Icon.png Ferrus Manus
UL Icon.png Roboute Guilliman
SAL Icon.png Vulkan
RG Icon.png Corvus Corax
Constantin Valdor
Zagreus Kane
Jenetia Krole
Simion Pentasian[26]
Nemo Zhi-Meng[26]
Cohran Hursula[26]
Harr Rantal[26]
SOH icon.png Horus Lupercal
EC Icon.png Fulgrim
IW Icon.png Perturabo
NL Icon.png Konrad Curze
WE Icon.png Angron
DG Icon.png Mortarion
TS Icon.png Magnus
WB Icon.png Lorgar Aurelian
AL Icon.png Alpharius† / Omegon
DA Icon.png Dark Angels
WS Icon.png White Scars
SW Icon.png Space Wolves
IF Icon.png Imperial Fists
BA Icon.png Blood Angels
IH Icon.png Iron Hands
UL Icon.png Ultramarines
SAL Icon.png Salamanders
RG Icon.png Raven Guard
Loyalist Imperial Army
Adeptus Mechanicus
Custodian Guard
Sisters of Silence
EC Icon.png Emperor's Children
IW Icon.png Iron Warriors
NL Icon.png Night Lords
WE Icon.png World Eaters
DG Icon.png Death Guard
TS Icon.png Thousand Sons
SOH icon.png Sons of Horus
WB Icon.png Word Bearers
AL Icon.png Alpha Legion
Traitor Imperial Army
Dark Mechanicum
The Lost and the Damned
Massive, Emperor forced to ascend to the Golden Throne,
Sanguinius KIA,
Ferrus Manus KIA
Malcador KIA
Massive, Traitors banished to the Eye of Terror,
Horus Lupercal KIA
Alpharius KIA

I am Horus, forged of the Oldest Gods, I am he who gave way to Khaos. I am that great destroyer of all. I am he who did what seemed good to him, And set doom in the palace of my will. Mine is the fate of those who move along this serpentine path

— Prophecy from the Book of Atum[9]

The Horus Heresy, also known as the Age of Darkness, was the first and most devastating civil war in Imperial history. Occurring in early M31 and lasting several years, it divided and nearly destroyed the fledgling Imperium. It marked the end of the Great Crusade and the encasing of the Emperor of Mankind into the Golden Throne.[1]


Preliminary Causes

Though the Heresy was ignited by the product of a conspiracy by the forces of Chaos, there were precipitating factors that helped push many of the Legio Astartes towards rebellion. The first was the Emperor's return to and seclusion on Terra, working on a secret project that he refused to share with any of his Primarchs, including his most favored son Horus, whom he had named Warmaster. This apparent abandonment of the Great Crusade, for something he would not even share with his sons bred mistrust, resentment, and disappointment towards the Emperor amongst many of the Primarchs.[2a]

Another contributing factor was the formation of an administrative body known as the Council of Terra. Many of the Primarchs viewed these human bureaucrats as usurping their rightful place as rulers of the Imperium they had fought so hard to create. Worse still, the Primarchs were denied a place on the Council and the notion of an Imperium dominated by human bureaucrats, not the sons of the Emperor and their Astartes Legions, became a cause of concern for many of the Primarchs.[2a]

In addition, the Emperor's disciplining of Lorgar and the Word Bearers was a contributing factor to the Heresy and the event which set it directly into motion. After Lorgar and the entire Legion were publicly humiliated, scolded, and forced to kneel in front of the Emperor for spreading their belief that the ruler of mankind was a divine being, the pious Word Bearers felt betrayed and desperately sought any power in the universe to worship. This eventually led Lorgar and his Legionaries to the Eye of Terror, where they pledged themselves to the forces of Chaos and began to conspire against the Emperor. Thus the Word Bearers had secretly become the first Chaos Space Marines. Secretly planning to make war on the Emperor, the Word Bearers quietly established Warrior Lodges with their Chaplains throughout the rest of the Astartes Legions. Though harmless at first glance, many of these lodges would become hotbeds of support for Horus' rebellion in the war to come.[3]

According to First Lord of the Imperium Malcador the Sigillite, the Heresy's causes may have been deliberately put into motion by both himself and the Emperor. According to Malcador, both deliberately agitated the Primarchs and turned them against one another, with the resulting war purging certain unmanageable Primarchs and their respective Space Marine Legions just as they had the earlier Thunder Warriors. This would lead humanity, not bio-engineered superhumans, as the rulers of the galaxy. However, the Ruinious Powers intervened before their plan could be fully formulated, leading to disaster in the Horus Heresy. This account may be either a partial or total lie, as Malcador himself seems to keep its validity ambiguous.[15]

Horus's Corruption

However, the Horus Heresy truly began after Warmaster Horus was wounded by the possessed Eugen Temba wielding the stolen Anathame on the moon of Davin, a place that was cursed by the foul Chaos God Nurgle. The wound caused by the blade refused to heal, despite Horus's super-enhanced immune system or the efforts of the Sons of Horus's best apothecaries. The Mournival took Horus to the Davinite Serpent Lodge, which they were told could heal him. Erebus and the Word Bearers had orchestrated the battle on Davin, unknown to all involved.[Needs Citation]

During the rituals, Horus's spirit was transferred into the Warp where Erebus, disguised as the Warmaster's closest friend Hastur Sejanus, showed him a terrible vision of the very future which his actions would bring about - the Imperium as a repressive, violent, and superstitious regime where the Emperor and some of the Primarchs (but not Horus) were worshiped as divine beings by the fanatical and ignorant masses of humanity. The Chaos Gods portrayed themselves as the victims of the Emperor's psychic might who had no interest themselves in controlling the material world. Horus, already having grown jealous and deeply resentful of his perceived poor treatment at the hands of his father, the Emperor, and was one of many afraid of the concept of a peace where all for which that they had fought was given to weak willed men whilst his legions were cast aside and left as peacekeepers. Horus therefore proved all too willing to accept the Ruinous Powers' false visions of an Emperor determined to make himself a god at Horus's expense.[Needs Citation]

But there was one thing no one had counted on: Horus's brother Magnus the Red, Primarch of the Thousand Sons, had continued to study the forbidden arts of sorcery, and was not about to let his brother fall to the powers of the Warp. The cyclopean giant appeared within Horus's vision, revealing the chaplain's identity and begging Horus not to give in to the temptations of Chaos. Unfortunately, Horus had decided that if anyone deserved to be worshipped as a god it was he, and not the Emperor. He accepted the offer of the Chaos Gods to join their cause and in return they healed his wound and granted him the powers of the Warp. The Chaos Gods' pact with Horus was simple: "Give us the Emperor and we will give you the galaxy."[2a]

Swaying the Legions

Renouncing his oath to the Emperor, Horus led his Legion into worship of the myriad Chaos Gods. Horus's genius was revealed as he converted half of the Legions, along with many regiments of the Imperial Army and several Titan Legions to his cause, revealing the Emperor to be as Horus saw him - a man undeserving of the praise and recognition of the human race.[2a]

Angron of the World Eaters, Fulgrim of the Emperor's Children and Mortarion of the Death Guard were the first Primarchs to side with the Warmaster. Horus found it easy exploit the Primarchs' flaws - Angron's frenzied love of violence was a match for Khorne; Fulgrim was corrupted by a daemon weapon of Slaanesh and its promise of unending perfection; Mortarion, already a close friend of his brother, was too easily persuaded, having been turned long before the Heresy through the efforts of his first captain Calas Typhon. Erebus had already vouched for the support of Lorgar and the Word Bearers, and Horus's plans came together with these legions at his side.[2a]

Of the other eventual traitors, Konrad Curze was due to face disciplinary action from the Emperor for his excessive bloodshed on Nostramo; Alpharius chose to join Horus after an ancient cabal of aliens revealed a prophecy to him that Horus's victory would cause the downfall of the Chaos powers; and Perturabo's cold nature and bitterness towards Rogal Dorn made him an easy target for corruption. Even with so many legions on his side, Horus was still aware that some of his brothers would never join him. Three of the most loyal Primarchs, Lion El'Jonson of the Dark Angels, Sanguinius of the Blood Angels, and Roboute Guilliman of the Ultramarines, were sent on missions far from Terra. The Blood Angels were sent to the daemon-infested Signus Cluster and the Ultramarines to Calth, where Kor Phaeron later attacked the loyalists with a large force of Word Bearers and millions of Chaos cultists. Unbeknownst to the Lion, a rebellion was soon to occur on his homeworld of Caliban while the bulk of his legion was bogged down battling the Gordian League.

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, Horus also ordered Fulgrim to turn Ferrus Manus to their cause, but the Phoenix underestimated the Gorgon's loyalty and barely escaped alive. Fulgrim promised he would deliver Manus's head to Horus in recompense.[2a]

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 Auretian Technocracy, delivering Adeptus Mechanicus support to the Warmaster's forces, and had corrupted a large portion of the Imperial Army and Navy.[9]

Burning of Prospero (004.M31)

Leman Russ and the Wolves of Fenris march on Tizca

Magnus, however, had yet to be dealt with. The Primarch was aware of his brother's fall and attempted to warn the Emperor of the impending betrayal. However, knowing that he would have to find a means of quickly warning the Emperor, Magnus decided to use his sorcery to deliver the message as an act of both desperation and vindication. The message penetrated the psychic defences of the Imperial Palace on Terra, shattering all the psychic wards the Emperor had placed on the Palace and destroying his secret project: a physical gate by which the Emperor intended to invade the Webway and take battle to the Eldar.[2a]

Magnus's brute force assault on the wards allowed the Warp and its myriad inhabitants to invade Terra. In the City of Sight, the tremendous rush of raw psychic energy obliterated the Choir Primus and shattered nearly every whisperstone. Millions died as their minds were burned out or daemons tore them apart. Warp storms consumed entire settlements. Shockwaves flattened structures around the world[5]. Having already outlawed the Primarch's use of sorcery and refusing to believe that Horus, his most beloved and trusted son, would betray him, the Emperor instead perceived the traitor to be Magnus and his Legion. The Emperor ordered the Primarch Leman Russ to mobilise his Space Wolves Legion and take Magnus into custody; Horus, however, persuaded Russ that Magnus was a threat and should not return to Terra alive. The Wolves of Fenris descended upon Prospero, destroying all in their path. Magnus, betrayed, defeated and forsaken by his beloved father, retreated into the Warp and pledged himself to Tzeentch. The Thousand Sons had never planned to join Horus, but the trap that the Changer of Ways had laid for the Red Sorcerer's legion led them to the Warmaster's side regardless. Meanwhile the catastrophe on Terra forced the Emperor to deal with a new crisis that consumed most of his attention. He led the Custodes and Sisters of Silence to deal with this, while he left management of the rebellion to Malcador and Rogal Dorn.[6]

Open Rebellion

Battle of Isstvan III (005-006.M31)[39]

The Luna Wolves battle the traitorous Death Guard in the Battle of Isstvan III

The first sign that Horus and his Legion had turned to Chaos was made evident when Horus virus bombed the rebel world of Isstvan III. The Planetary Governor of Isstvan III had declared his independence from the Imperium and the Council of Terra charged Horus with retaking 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, Emperor's Children, 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 Isstvan System.[2b]

Horus had a plan by which he would destroy all loyalist elements of the Legions at his command. After a lengthy bombardment, Horus dispatched all Loyalist Marines down to the planet, ostensibly to bringing it back into the Imperium. At the moment of victory, however, the loyalist marines were betrayed: with a cold snarl of "Let the galaxy burn!, Horus ordered his ships to open fire on Istvann III and virus bombs began to rain down on the planet. However, some marines loyal to the Emperor had remained on board their ships, and as Isstvan III died, these soldiers fought desperately to warn their brethren on the surface. Their sacrifice saved many marines, as they were able to take shelter before the virus bombs struck. The population of Isstvan III received no such protection. Twelve billion people died almost immediately. The psychic shock of so many simultaneous deaths shrieked through the Warp, alerting the Emperor that something was terribly wrong and informing the Chaos Gods that Horus was now theirs. A contingent of loyalists led by Captain Garro of the Death Guard escaped the fleet orbiting Isstvan III aboard the damaged Eisenstein, fleeing to Terra to warn the Emperor.[2b]

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 fifty companies of World Eaters. 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 Isstvan 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, forced Angron to withdraw his forces, and ordered a systematic orbital bombardment that killed Isstvan III's last brave survivors.[2b]

The Court of Horus at the height of the Heresy. From left to right: Erebus, Kelbor-Hal, Maloghurst, Abaddon, Horus, Red Angel, Ahriman, Ingethel, Fulgrim

Flight of the Eisenstein

Main article: 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 Isstvan system into the Immaterium. The Eisenstein was badly damaged during its escape from Isstvan 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.[28]

The remaining crew of the Eisenstein, now aboard Primarch Dorn's fortress-monastery Phalanx, was able to reach Terra (after Dorn's fleet destroyed the Eisenstein to ensure no Chaos taint remained), allowing the loyal marines to report the extent of the atrocities that had occurred in the Isstvan system. It was said in later millennia that without this warning, the Imperium would have faced even greater difficulties in responding to Horus's next moves although his warning may have enabled Horus to enact the drop site massacre.[28a]

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. Others believe some of these men formed the nucleus of the elite Space Marines Chapter later known as the Grey Knights, for Malcador the Sigillite 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.[Needs Citation]

Signus Campaign (004-006.M31)[39]

Sanguinius and Ka'Bandha battle on Signus Prime

At the Signus Cluster Sanguinius and the Blood Angels narrowly avoided corruption at the hands of Daemonic forces under Kyriss the Perverse and Ka'Bandha.

Schism of Mars (005-006.M31)

Battlefield Mars

On Mars, the Warmaster's allies (Dark Mechanicum), led by the Fabricator-General Kelbor-Hal, begin the Schism of Mars with the unleashed of a Chaos scrapcode, from the forbidden Vaults of Moravec, against the different forges of the planet. With this action the civil war of the Adeptus Mechanicus begins.[30a]

The damage of the scrapcode causes the devastation of the majority of the installations and disrupts the planet's communications. Within the confusion, the Dark Mechanicum begins the conquest of the planet. However, they discovered that some Forges remain relatively intact due to his more advance security system. The traitor forces begin the assault against the pockets of resistance with the immediate siege of one of these Forges, leaded by Ipluvien Maximal. Owerhelmed after resisting for some time, the Tech-Priest detonated the reactors of his own forge to deny the victory of the traitors. In a brief time all Mars became a bloody battlefield where the devastation of the battles costs a great damage of the industrial infrastructure and the repository of knowledge of the planet.[30]

Another of the main forges that resisted the scrapcode's attack was the Magma City, leaded by Koriel Zeth, a loyal member of the Mechanicum. Kelbor-Hal to justify his attack against the forge, declares Koriel an heretic for her denial of the Machine God cult. After resisting the first attacks, She was owerhelmed by the traitors and, such as Maximal, she decided to detonate her own forge to deny its use by the traitors.[30]

After this combats, the loyal forces were reinforced with four companies of the Imperial Fists Legion and imperial army auxiliar, leaded by Captains Sigismund and Camba-Diaz.[30b] However, due to the great numbers of the Dark Mechanicum forces, it was impossibile to turn the tide of the battle. After acknowledge the situation, Sigismund orders the loyal forces to take all munitions, armors and equipment possible with them before evacuate the remaining loyal forces from the planet.[30]

The conquest of Mars by the Warmaster's allies was a devastate loss for the loyalist forces. Nevertheless, Rogal Dorn, Primarch of the Imperial Fists, orders a blockade of the Planet to contain the traitors. The blockade would resist until the arrive of the Warmaster's forces for the Siege of Terra in 014.M31.[31a]

Drop Site Massacre (006.M31)

The Drop Site Massacre

After ridding himself of all suspected loyalist members within the three Legions under his direct command, Horus chose Isstvan V as his command post and prepared a trap for his former brothers and their Legions.[Needs Citation]

Agonizing over the betrayal of his most beloved son, the Emperor ordered the deployment of seven full Space Marine Legions against him. Their orders were to take Horus and the Primarchs allied with him into custody and bring them back to Terra to explain their actions. Unbeknownst to the Emperor, four of the Primarchs and their Legions chosen for this task had already turned against him, forming a "fifth column" which would strike against the loyalists at the most decisive moment.[2b]

The initial naval operations seemed to go well for the loyalists. The Imperial Navy gained orbit over Isstvan V and the Legions proceeded with their planetary deployment. Under the overall command of Ferrus Manus, three whole Legions took part in the first wave of landings; the Salamanders lead by Vulkan, the Raven Guard under Corax, and Manus's own Iron Hands. Horus had foreknowledge of the location of the loyalist drop site and his forces mauled the Legions during their landings, keeping them pinned down and unable to advance.[2b]

Ferrus Manus engaged Fulgrim in personal combat, only to die at his hands while the Emperor's Children butchered the Iron Hands. The loyalists retreated towards the apparent safety of their brothers in the second wave, hoping to gain reinforcement; what happened next took them completely by surprise. The four Legions of the second wave - The Night Lords of Konrad Curze, the Iron Warriors of Perturabo, the Word Bearers of Lorgar, and the Alpha Legion of Alpharius — already seduced to the cause of Horus, opened fire on their unsuspecting brothers, slaughtering them wholesale. This orgy of carnage would later become widely known as the Istvaan V Drop Site Massacre. A phrase attributed to the Warmaster himself can easily summarise the entire battle: "When the traitor's hand strikes, it strikes with the strength of a Legion." After the battle, Fulgrim presented the head of Ferrus Manus to Horus as a trophy.

Only a small number of loyalist Space Marines, bearing the gene-seed of their fallen brothers and carrying the critically wounded Corax, managed to escape. They fled back to the Raven Guard's homeworld, Deliverance, to tend to their wounds and alert the Emperor. In a single stroke Horus had crippled three Legions, killed one Primarch in battle, left another severely wounded, and a third (Vulkan, who survived due to being a Perpetual) was captured and imprisoned by his brother Konrad Curze.[29] It was disastrous news for the Emperor and the Imperium.[2b]

The Rebellion Spreads

Horus' Rebellion spreads across the Imperium

After the victory at Isstvan V, Horus' rebellion spread like wildfire across the greater Imperium. Traitor forces conducted their own "Dark Compliances" of once-loyal worlds, giving them the choice of submission or destruction in a twisted mimicry of the Compliances Great Crusade. Nowhere was this more evident than the swathe of the northern Imperium Horus carved out for himself dubbed the Dark Empire.[41a]

The Sundered and the Blackshields

As chaos erupted across the Galaxy, many new ad-hoc armies and brotherhoods spawned. The Shattered Legions was a term attributed to a broad range of Astartes formations, but most notably the Raven Guard, Salamanders, and Raven Guard following the Drop Site Massacre which regrouped for their own bitter war of vengeance against the Traitors.[41b]

As both loyalist and traitor armies were cutoff behind enemy lines or without support for extended periods, they found themselves acting alone. The brutal realities of the war caused some to break and act to their own desires. Some resurrected ancient resentments against their former brethren, others pursued petty vengeance for percieved slights of honor. Others became consumed by the forces they had unleashed, shredding reason and honor and taking up the mantle of reaver. Individual warriors up all the way to entire Legion contingents became swept up in this madness, which were eventually given the umbrella title of Blackshield. Many of these warriors were broken in both mind and spirit, driven to their new title by desperation. Some Blackshield formations consisted of both loyalists and traitors, disregarding the greater galactic turmoil to pursue their own angles.[41b]

Wars For Paramar (006-011.M31[39])

After the victory of the Drop Site Massacre, Horus orders his forces to capture the world of Paramar V for its strategic position. The world, laid on the northern edge of Segmentum Solar, was a staging area for Expeditionary Fleets during the Great Crusade and its conquest was a first step of the Warmaster’s campaign against Terra.

The forces of the Warmaster, consisted in elements of the Alpha Legion, Legio Fureans and Dark Mechanicum, launch an invasion of the planet. After an initial bloody combat, the traitors seized most of the planet with the conquest of the Landing Zone Secundus. However, the loyalists defenders, formed from the loyal 77th Grand Company of the Iron Warriors, Legio Gryphonicus and Mechanicum forces, make a stubborn defence on the primary spaceport and take heavy losses to Legio Fureans. The defence of the loyalist lasts until the second attack of the Alpha Legion, who turns the tide of the battle and conquers the last bastion of the loyalist, securing the planet for Horus.

Manachean War (006-008.M31)

During the Manachean War, Horus himself led forces to conquer the Coronid Deeps.[32]

The Siege of Cthonia (006-014.M31)

Faced with Horus' treachery, Rogal Dorn dispatches an Imperial Fists fleet to besiege the nearby world of Cthonia, homeworld of the Sons of Horus. The brutal siege lasts all the way until the final phase of the Heresy.[39]

Battle of Phall (007.M31)

The Imperial Fists and the Iron Warriors in battle over the Phall system

Following the news of the traitor victory at Isstvan V, Rogal Dorn dispatched a large Imperial Fists "retribution fleet" to bring them to heel. However, they were assailed by a large Iron Warriors fleet in the Phall System.[2f]

Battle of the Alaxxes Nebula (007.M31)

As the Space Wolves reel from the fighting on Prospero, they are ambushed by the Alpha Legion within the Alaxxes Nebula. Taking heavy losses, the Space Wolves are able to hold off the traitors until Dark Angels reinforcements arrive.[39]

First Siege of Hydra Cordatus (~007.M31)

At the First Siege of Hydra Cordatus, Perturabo led the Iron Warriors against the Imperial Fists.[33]

Furious Abyss and Battle of Calth (007.M31)

Roboute Guilliman takes the battle to the void above Calth

During the developments at Prospero, Horus's rebellion would be further strengthened by Magnus the Red and his Legion, the Thousand Sons, now servants of Tzeentch. With nine Legions and much of the Adeptus Mechanicus behind him, Horus quickly struck towards Terra after gaining the powers of the Emperor after the Battle of Molech.

Meanwhile in Ultramar, the Word Bearers under Lorgar launched a devastating surprise attack against the Ultramarines as the gigantic Battleship Furious Abyss attempted to attack Macragge. While the Ultramarines took grievous losses at Calth, the Furious Abyss was destroyed and the Legion survived. Roboute Guilliman would now have to contend with the Shadow Crusade of the Word Bearers and World Eaters.[36][37]

Thramas Crusade (007-010.M31)[39]

To hold up The Lion, Horus dispatched the Night Lords to rampage throughout the Imperium to draw the attention of his Dark Angels in the Thramas Crusade.

Shadow Crusade and Crusade of Iron (007-009.M31)

Lorgar and Angron with their legions fight against the Ultramarines during the Shadow Crusade

The Ultramarines were still reeling from their battle with the Word Bearers at the Battle of Calth but subsequently faced the combined forces of Lorgar and Angron in the Shadow Crusade as they rampaged throughout Ultramar. Meanwhile, Loyalist Titan Legions launched a punitive counterattack in what became known as the Crusade of Iron.[38]

The Khan's Decision (007.M31)

Jaghatai Khan and the White Scars Legion.

To occupy the bulk of remaining loyalist forces, Horus commanded the Alpha Legion to bog down the Space Wolves and to jam the communications of the White Scars, who were unaware of the Heresy, fighting in a long campaign against the orks of the Chondax System. For this purpose the Alpha Legion uses a strange pylon, located on the Tenebrae 9-50 Installation in the Octiss System, to manipulate the Warp and the communications of the Vth Legion. However, the plan failed when Omegon dispatched a small team, leaded by Sheed Ranko, to neutralise the device. This action let the White Scars to recover their communications with the rest of the Imperium and discover the news of the Heresy.

After discovering the news, the Khan initially refused to throw his lot in with either side. Instead, he sought to undercover the truth for himself at Prospero. Upon discovering the ruin the Khan was still conflicted, leading to an attempted coup by Horus sympathsizers in his own Legion as well as an attempt by Mortarion to actively recruit him. Ultimately the Khan rejected the Traitor's offer and made to join the loyalist war effort.[34] The White Scars would go on to wage a guerrilla behind Horus' lines for the next several years, taking grievous losses.[2e]

Capture of the Perfect Fortress (008.M31)

An impregnable fortress created by Primarchs Perturabo and Fulgrim comes under futile attack by an Imperial Army cohort, who are run down and butchered by the Emperor’s Children. The defenders then turn to find the Raven Guard under Corax occupying their vacated fortress, who swiftly turn the powerful defensive weapons on their careless former brothers.[39]

Mezoan Campaign (008.M31)

The Mezoan Campaign saw Mechanicum and a hybrid Alpha Legion-Iron Warriors force clash over control of the vital Forge World of Mezoa.[31b]

The Siege of Baal (008-013.M31)

Baal, homeworld of the Blood Angels, has become a refuge for many loyalists fleeing Horus' forces. Seeing this safehaven as a threat, the world is attacked by a combined force of Sons of Horus, Emperor's Children, and Dark Mechanicum. After years of siege, the traitor assault is repulsed with heavy losses on both sides.[39]

The Battle of Vanaheim (008-009.M31)

The Iron Warriors under Perturabo launch a daring void assault against the orbital hives of Vanaheim, seizing them from the Mechanicum. Subsequent loyalist counterattacks end in failure.[39]

The Path of Heaven

Jaghatai Khan and the White Scars Legion fight against Slaanesh daemons on their way to Terra

After the discovery of the Dark Glass and the subsequent Battle of Catallus, the White Scars managed to return to Terra to defend the capital world with their force[2e][4].

The Breaking of Anvillus (009.M31)

The vital Forge World of Anvillus falls into devastating civil war that sees both sides largely destroyed.[39]

Battle of Molech (009.M31)

Following the Battle of Dwell and a failed assassination attempt on Horus by Shadrak Meduson, the traitor Warmaster regained memories sealed by the Emperor regarding the world of Molech. Horus speculated that great power lay on Molech, and wished to claim it in order to usurp his father. In the subsequent battle, Horus gained access to a Warp gate and gained radical new psychic abilities.[35]

The Formation of Imperium Secundus (009-011.M31)

Roboute Guilliman proclaims Sanguinius as Imperator Regis of Imperium Secundus

Despite the traitor defeat on Calth, Erebus was successful in creating the Ruinstorm which threw the Astronomican into disarray and rendered navigation and communication difficult. The Blood Angels and Dark Angels under their respective Primarch's sought Terra, but were unable to navigate the Ruinstorm and instead locked onto the Pharos beacon, ending up in the Realm of Ultramar instead. As a result, Roboute Guilliman feared the Imperium lost and created a second empire, Imperium Secundus, as a contingency with Sanguinius as its Imperator Regis and Lion El'Jonson as its Lord Protector.[6]Early tests for Imperium Secundus came from both the Battle of Sotha and the unleashing of Konrad Curze on Macragge.

The Siege of Inwit (009-013.M31)

Dozens of Traitor fleets assail the Inwit Cluster, seeking to capture the Homeworld of the Imperial Fists. The bloody siege continues until Horus repositions forces for the attack on Terra.[39]

The Battle of Tallarn (010-012.M31)

Perturabo invaded the world of Tallarn, beginning one of the largest armored conflicts in galactic history.

Nocturne and the Journey of Vulkan (~010.M31)

Following the apparent death of a maddened Vulkan on Macragge, the Primarch is brought back to their homeworld of Nocturne by his sons. After fending off a Death Guard invasion, Vulkan is apparently resurrected and begins his pilgramage to Terra through the Webway.[40]

The Cataclysm of Iron (012-015.M31)

A concentrated string of Forge Worlds known as the Belt of Iron is wracked by fighting between the Loyalist and Dark Mechanicums. Not even the intervention of the Dark Angels can bring a quick end to the war, which continues beyond the Heresy itself.[39]

Final Phase (010-014.M31)

The Solar War (010-014.M31)

After years of bitter fighting, Horus and his forces finally arrived at Terra, capital of humanity. For several years previous, traitors had been wresting control of the Sol System from the Imperial Fists in the Solar War. During these battles, the Alpha Legion struck at Pluto and Alpharius himself was seemingly killed by Rogal Dorn.[13]

The Dissolution of Imperium Secundus (011.M31)

The Imperium Secundus was constantly undermined thanks to the political clashes between Guilliman and Lion El'Jonson, with Sanguinius proving unable to negotiate settlements between the two.[19] Due to the visions of both Sanguinius and Konrad Curze of the Emperor, it became apparent that he still lived and Terra still endured. This, along with the many disagreements between its ruling triumvirate, resulted in the dissolution of Imperium Secundus. Sanguinius, Roboute Guilliman, and Lion El'Jonson attempted to breach the Ruinstorm to reach Terra, but in the end only Sanguinius and the Blood Angels were successful.[14]

The Battle of Trisolian and the Wolf Cull (012.M31)

Shortly after the arrival of Sanguinius on Terra, Leman Russ left with the intent on confronting Horus himself. Thanks to runes planted by infiltrating Knights-Errant during the Battle of Molech the Space Wolves were able to track the location of the Vengeful Spirit, and Russ and Horus engaged one another in a duel as battle raged around them. Russ was badly wounded, but in turn wounded Horus with the Spear of Russ, cleansing much of the corruption that had befallen the Warmaster since Molech. However the battle cost the Space Wolves dearly, and they fled to Yarant with Russ in a comatose state.[16] The Wolves narrowly avoided destruction at the hands of Sons of Horus First Captain Ezekyle Abaddon thanks to Corax and the Raven Guard.[16]

Battle of Beta-Garmon (012-013.M31)

Horus' armies had by now finally arrived at the gates of the Sol System, and sought to move onto the Imperium Throneworld. However to do this, they would first have to capture the strategically vital Beta-Garmon Cluster. The resultant Battle of Beta-Garmon was one of the largest of the Heresy, seeing massive casualties on both sides. Particularly hard hit were the Titan Legion's, which led to the battle being referred to as the Titandeath. However in the end Horus' forces prevailed, despite the Warmaster himself falling to wounds inflicted at Trisolian by Leman Russ.[17a]

The Lion's Purge (012-013.M31)

Freed from the Ruinstorm, the Dark Angels under Lion El'Jonson conduct a purge of traitor worlds, destroying Chemos, Barbarus, and ultimately Cthonia.[39]

The Muster on Ullanor and Lorgar's coup (013.M31)

After the titanic Battle of Beta-Garmon, Horus' fleet was within range of the Sol System and mustered their forces on Ullanor. Horus during this time was still suffering wounds inflicted by Russ at the Battle of Trisolian, and the traitor war effort would have fallen apart had it not been for Maloghurst who gave his life to restore the Warmaster. During the muster of the Traitor Primarch's at Ullanor, Lorgar revealed that he saw Horus as weak and doomed to fail and attempted to usurp him. However Horus defeated the coup, and exiled Lorgar from his sight. Alpharius apparently quit the traitor war effort after giving the Warmaster a detailed map of the Sol System defenses, but Horus still mustered Angron, Magnus, Perturabo, and Fulgrim to his side on Ullanor as well as forces from the Night Lords and Word Bearers.[17b]

Meanwhile, the Alpha Legion defies Horus' orders and instead sets out to delay Roboute Guilliman's advance on Terra.[39]

The Fall of the Death Guard (013-014.M31)

Meanwhile, Mortarion and the Death Guard were fully corrupted inside the Warp by Nurgle thanks to sabotage by First Captain Calas Typhon. When the re-emerged from the Warp in the Sol System, they had become a horrifying army of Plague Marines.[2]

The Siege of Terra (014.M31)

Horus and the Emperor battle on the Vengeful Spirit

In 0000014.M31, the first day of Primus, Horus' armada at last arrived at the Sol System. During the final intense phase of the Solar War, the traitors captured the Solar System from loyalist forces despite the best efforts of Rogal Dorn to stall until the arrival of reinforcements from Roboute Guilliman and Lion El'Jonson.[25] Once within range of Terra, Horus and his forces destroyed Luna's naval bases and within thirty days had destroyed the Terran system's defences. Terra was bombarded and devastated. The corrupted Marines from the Sons of Horus, Death Guard, World Eaters, Emperor's Children, Iron Warriors, Thousand Sons, Word Bearers, and Night Lords eventually landed on Terra, experiencing heavy resistance from the defenders which were led by the Imperial Fists, Blood Angels, and White Scars. Vast amounts of traitor Imperial Army, Dark Mechanicum, Chaos Cultists, and Daemonic forces joined the traitor Astartes in their assault on Terra. The loyalists were outnumbered and the battle for Terra turned into a siege of the Imperial Palace. By the fifty-fifth day the rebels had reached the walls of the Inner Palace but Sanguinius managed to hold the Eternity Gate despite a vicious assault led by the Bloodthirster Ka'Bandha. Eventually a stalemate set in with not even the siegecraft of Perturabo and the Iron Warriors being able to break the tide. Horus, who had remained in orbit aboard his battle barge, was at that point warned that the Ultramarines and Dark Angels were returning to Terra and would arrive shortly. If this were to happen, Horus's advantage in numbers would be eliminated and he faced the prospect of attacks to his rear. In a final gambit he deactivated the Void Shields protecting the Vengeful Spirit to lure the Emperor in a final battle that would decide the war.[2e] At the same time, Typhus led a Death Guard assault against the Astronomican, seeking to stop its reactivation by Corswain and his Dark Angels as well as Euphrati Keeler and Sigismund.

Leaving Malcador the Sigillite behind to maintain the Golden Throne and thus the seal on the ruptured Imperial Webway, The Emperor saw this opportunity and teleported to the Warmaster's flagship Vengeful Spirit with Sanguinius and Dorn, Terminator-armoured marines of their Legions, and a number of Custodes. The Emperor's forces were scattered through the ship upon arrival and forced to battle their way to find each other. Sanguinius found Horus first. Horus was at the height of his powers, augmented with the blessings of all four Chaos Gods and the god-like powers he had acquired during the Battle of Molech, and Sanguinius was slain. Horus stood over the Primarch's body as the Emperor found him. After a long and grueling battle, the Emperor was successful in slaying Horus, but He Himself was mortally wounded. The Emperor survived long enough to be transferred to the Golden Throne, with Malcador having sacrificed his own life to sustain the device in His absence. With Horus dead, First Captain of the Sons of Horus Ezekyle Abaddon took command of the Legion and retreated, causing a general rout among the traitor forces as Guilliman's reinforcement fleet finally arrived thanks to the successful reactivation of the Astronomican. The assault on Terra was broken, but at great cost.[2e]


The Emperor's final command began the Great Scouring. Under the leadership of the remaining loyalist Primarch's the forces loyal to Horus were hounded into the Eye of Terror and locations such as the Isstvan System sterilized. All records and the remaining homeworlds of the traitor legions were destroyed. Inside the Eye, the remaining Traitor Primarch's, now nearly all Daemon Princes, became detached from the affairs of the Materium and let their children fend for themselves.[21] Without the Primarch's, the traitor legions themselves engaged in a bitter civil war until Ezekyle Abaddon, assuming the epithet "the Despoiler," would become closest the traitor legions would have to a unified leader and lead a number of Black Crusades into the Imperium in the millennia to come.[20]

With the Emperor now indisposed, Roboute Guilliman took the mantle of Lord Commander of the Imperium and worked his brothers to introduce sweeping reforms to prevent another major rebellion from occurring, most notably the implementation of the Codex Astartes and dividing the Imperial Army into the Imperial Guard and Imperial Navy.[18a] Two agencies left behind by Malcador before his death, the Inquisition and Grey Knights, helped to maintain the new order and prevent new heresies.[23] Over the course of the Great Scouring, all of the remaining loyalist Primarch's either went missing, were presumed killed, or in the case of Guilliman himself put into stasis to avoid death due to his mortal wounding by Fulgrim at Thessala.[22]

Ultimately, the Horus Heresy was instrumental for the ten-thousand year decay that has since set into the Imperium. The Emperor's grand ambition, the Imperial Webway, was abandoned and Chaos continued to plague humanity. The hope and reason of the Imperial Truth was gradually replaced by the repression and superstition of the Imperial Cult which now worships the Emperor, still kept alive upon the Golden Throne through the daily sacrifice of a thousand Psykers, as a god.[24] Technologies from the Great Crusade-era were lost over time, and eventually even the Heresy itself became the subject of myth to the citizens of the Imperium.

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