The Great Primarch Civil War (Horus Heresy)

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The Great Primarch Civil War was a galaxy-spanning war that engulfed the entire galaxy for 23 Terran Years. The outbreak marked the end of the Great Crusade and the dream of peace that was in the hopes and dreams of the Imperium of Man. The Civil War undid the work that Mankind had fought so valiantly for, as their goal of reuniting the scattered colony worlds of Humanity in the Milky Way Galaxy under a single government led to the division of the Imperium's greatest warriors and the start of Chaos' great wars.
The civil war began following the corruption by Chaos of the Imperial Warmaster Horus Lupercal, the primarch of the Sons of Horus Legion and the most beloved genetic son of the Emperor. The daemon that corrupted him was Ra'Kaba and as a result transformed the armies of Chaos into the greatest force in the Galaxy. This daemon would also be the reason they lost the war and failed in their ultimate goal, the death of the Emperor. The Chaos Gods manipulated Horus by granting him everything he ever wanted. All his ambitions, desires and hatred led him to becoming the Champion of Chaos.
Horus slowly convinced more than half of the other primarchs and Space Marine Legions, as well as large swathes of the Imperial Army and the forces of the technophilic Mechanicum, to turn Traitor alongside him and to declare a war that would dwarf all that came before it and all that would come.
For a nightmarish 23 years, the greatest war to ever be waged destroyed the Imperium of Man. All corners of the Imperium would be shattered and left nigh unrepairable. The Halo Stars, the Ghoul Stars, the 500 worlds of Ultramar, the Red Scar Region; nothing that Mankind had conquered and inhabited were untouched by war. For those sector and planets that had or were still home to the Primarchs and their legions, it was the worst form of death sentence.
The conflict was fought across the Milky Way Galaxy early in the first century of the 31st Millennium and resulted in more than 11.7 trillion dead in the immediate aftermath of the Siege of Terra, with 3 trillion more in the following crusades to cleanse and destroy all that chaos held within the Galaxy.
The Great Primarch Civil War resulted in an all-out brawl in the Throne Room, which left 6 of the 13 Primarchs present killed and only concluded with the death of the sacrifice of the Lord of Ultramar and the Primarch of the XIII Legion known as the Ultramarines, Roboute Guilliman, and the retreat of the Chaos Primarchs and their legions from Terra.
== The First To Fall ==
=== The Pilgrimage of Lorgar ===
Prompted by First Captain Kor Phaeron and the XVII Legion's First Chaplain Erebus, both secret devotees of the Chaos Gods through Colchis' Old Faith, Lorgar journeyed with his Word Bearers Legion's Chapter of the Serrated Sun to what was then the fringes of known Imperial space as part of the 1301st Expeditionary Fleet of the Great Crusade. At this time, Lorgar had not yet fallen to the corruption of Chaos, though he had turned against the Emperor of Mankind as a deity no longer worthy of his worship. Lorgar believed that the Emperor was wrong to condemn Mankind's natural instinct to seek out the divine as an unworthy superstition and he intended to discover if there were truly deities worthy of humanity's respect. To this end, though Lorgar no longer had any love or loyalty for the Emperor, he and his XVII Legion rejoined the Great Crusade but did so only so their efforts could serve as a front for their pursuit of the Pilgrimage of Lorgar.
The Word Bearers were also accompanied on this Pilgrimage by 5 members of the Legio Custodes who had been set by the Emperor to watch over everything the Word Bearers did to prevent them from falling back into error once more. The Word Bearers' pursuit of any scrap of information that could be found on the Primordial Truth or the nature of the place where Gods and mortals could mingle ultimately led the 1301st Expeditionary Fleet to the Cadia System near the largest permanent Warp Storm in the galaxy, later known to the Imperium as the Eye of Terror. The Expeditionary Fleet's Master of Astropaths advised Lorgar that unusual "voices" in the Warp were heard in the vicinity of the great Warp rift, voices that spoke directly to the Primarch as well, which were the voices of the Chaos entities within the Immaterium. It would be in the Cadia System that Lorgar would learn that his suspicions had been correct and that the shape of all of the religions across the galaxy that possessed so many similarities to the Colchisian Old Faith were not artefacts of Mankind's collective unconsciousness, but expressions of worship in the universal truth that was Chaos.
The so-called "Primordial Truth" of the existence of Chaos changed Lorgar and the Word Bearers forever as they were exposed to the Ruinous Powers and slowly corrupted, the first of the Space Marine Legions to worship the Chaos Gods and become Traitors to the Emperor in their hearts. Lorgar and the Word Bearers spent the remaining years of the Great Crusade attempting to enlighten humanity about the true spiritual nature of Creation, ultimately resorting to manipulation and deception to sway nine of the Primarchs to the cause of Chaos as their Gods demanded, the most notable being the Warmaster Horus. When it became clear that Mankind could not be enlightened by Chaos without first being forcibly weaned at a great price in blood from the Emperor's false Imperial Truth, Lorgar would go on to willingly help orchestrate the terrible Battle of Isstvan III and the Drop Site Massacre at Isstvan V as well as the larger Horus Heresy itself. When Horus openly declared his rebellion against the Emperor, the Word Bearers were one of the first Legions to support him and his cause. The worlds they had conquered since their conversion to Chaos also joined the side of the Traitors, having been secretly corrupted to the worship of the Ruinous Powers in the final days of the Great Crusade.
=== Fall of Horus ===
During the Great Crusade, it became apparent that the Primarchs were far from the perfect specimens of humanity they were intended to be. Although each Primarch was physically and mentally god-like compared to a baseline human being, they harboured the flaws of vanity, egotism, hunger for power, jealousy, arrogance, insecurity and all the other sins of the human character.
As the Warmaster, Horus took over command of the Great Crusade, and accepted his new duties with earnest dedication. However, there was much dissension in the ranks of the Primarchs and other parties in the Imperium over the Emperor's decision to withdraw from the campaign and return to Terra as well as to reorganise the administration of the Imperium. Only a handful of the Primarchs, among them a scheming Lorgar, remained steadfast beside the Warmaster during this period of conflict. Horus also disagreed with many of the decrees passed by the newly established Council of Terra, intended to shift the burden of taxation and administration onto the newly-conquered ("Imperial Compliant") worlds. Even worse, Horus came to believe in his heart that he was failing his father, and was deeply wounded that the Emperor had revealed to none of the Primarchs, not even his most favoured son, why he had secluded himself upon Terra and the truth behind his secret Webway Project. These seeds of bitterness, resentment and frustration grew, and would soon bear deadly fruit.
It was on the moon of the world of Davin that Horus' 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 towards the service of the Chaos Gods.
During a battle against Chaos-spawned undead on Davin's moon, whose Planetary Governor, Eugen Temba, had been corrupted by the forces of the Chaos God Nurgle, Horus was poisoned by a xenos blade dedicated to Nurgle known as a Kinebrach Anathame that had been stolen from the human civilisation of the Interex by Erebus after Horus and the Luna Wolves of the 63rd Expeditionary Fleet had made a disastrous first contact with them. Erebus then gifted the weapon to the Chaos-corrupted form of the Imperial Army commander Eugen Temba who the Warmaster had left behind to govern Davin sixty years before. Temba had turned to the worship of Nurgle in the interim, being transformed into a bloated mutant and killing off most of his Imperial Army garrison in the process, transforming them into undead Plague Zombies that the Luna Wolves were forced to mow down in waves. Horus personally faced off with the mutant that had been Temba aboard the grounded ruins of his Imperial Cruiser. In the course of that battle, the potent living metal of the Chaos blade wielded by the plague-infused monstrosity left Horus with a bleeding, toxic wound in his shoulder that his Legion's Apothecaries could not heal despite all the advanced technology available to them. Seeing his chance to further the designs of Chaos, Erebus next persuaded the Luna Wolves' warrior lodge to allow a group of Davinite shamans -- Chaos Cultists all -- located on the surface of Davin at the Temple of the Serpent Lodge to heal him. The Luna Wolves, besides themselves with grief and the fear that their beloved Primarch would die, agreed to the suggestion, despite its direct violation of the creeds of the Imperial Truth.
During the dark rituals that followed within the temple, Horus' spirit was transferred from his body into the Immaterium. There, he bore witness to a nightmare vision of the future. He saw the Imperium of Man as a repressive, violent theocracy, where the Emperor and several of his Primarchs (but not Horus) were worshiped as Gods by the masses. While this vision of the Imperial future granted by the Chaos Gods was a true one, it was ironically an outcome largely created by the Warmaster's own actions. The Dark Gods portrayed themselves as victims of the Emperor's psychic might, and claimed that they had no real interest in the happenings of the material world. They healed his grievous wound and filled him with the powers of the Warp, and a daemon known as Ra'kaba. Renouncing his oath to the Emperor, Horus led his Legion, renamed the Sons of Horus, into worship of the myriad Chaos Gods in the form of Chaos Undivided. The daemon was the reason for his betrayal, if Horus was acting on his free will the Horus Heresy would've been found at its roots years before. He then sought to turn many of his fellow Primarchs to the service of Chaos, and succeeded with Perturabo of the Iron Warriors, Fulgrim of the Emperor's Children and Alpharius Omegon of the Alpha Legion, who were the first of many to follow, along with many regiments of the Imperial Army and several Titan Legions of the Adeptus Mechanicus,
== The Betrayal ==
=== Isstvan III ===
Unknown to the Emperor, the Word Bearers Legion had been devoted to Chaos Undivided for years before the events on Isstvan III. The Imperial Planetary Governor of Isstvan III, Vardus Praal, had been corrupted by the Chaos God Slaanesh whose cultists had long been active on the world. Praal had declared his independence from the Imperium, and practiced forbidden sorcery, so the Council of Terra charged Horus with the retaking of that world, primarily its capital, the Choral City. This order merely furthered Horus' plans to overthrow the Emperor. Although the four Legions under his direct command -- the Sons of Horus, the Emperor's Children, the Iron Warriors and the Alpha Legion -- had already turned Traitor and now pledged themselves to Chaos, there were still some Loyalist elements within each of these Legions that approximated one-third of each force; many of these warriors were Terran-born Space Marines who had been directly recruited into the Astartes Legions by the Emperor himself before being reunited with their Primarchs during the Great Crusade. Horus, under the guise of putting down the religious rebellion against Imperial Compliance on the world of Isstvan III, amassed his troops in the Isstvan System.
Horus had a plan by which he would destroy all the remaining Loyalist elements of the Legions under his command, a plan that would ultimately unfold into the nightmare of what Imperial scholars would later name the Isstvan III Atrocity. After a lengthy bombardment of Isstvan III, Horus dispatched all of the known Loyalist Astartes down to the planet, under the pretense of bringing it back into the Imperium. At the moment of victory and the capture of the Choral City, the planetary capital of Isstvan III, these Astartes were betrayed when a cascade of terrible virus-bombs fell onto the world, launched by the Warmaster's orbiting fleet. Captain Saul Tarvitz of the Emperor's Children, however, was aboard his Legion's flagship Andronius and discovered the plot to wipe out the Loyalist Astartes of the Traitor Legions. He was able to reach the surface of Isstvan III despite pursuit and warn the Loyalist Space Marines he could find of all four Legions of their impending doom. Those that heard or passed on Tarvitz's warning took shelter before the virus-bombs struck. The civilian population of Isstvan III received no such protection: eight billion people died almost at once as the lethal flesh-dissolving virus called the Life-Eater carried by the bombs infected every living thing on the planet. The psychic shock of so many deaths at one time shrieked through the Warp, briefly obscuring even the Astronomican. The Primarch of the Iron Warriors, Perturabo, realising that the virus-bombs had not been fully effective at eliminating all the Loyalists, flew into a rage and hurled himself at the planet with 50 companies of Traitor Marines. Discarding tactics and strategy, the Iron Warriors Legion's Traitors worked themselves into a frenzy of destruction and death as they battered and crushed Loyalist fortifications one after another. Horus was furious with Perturabo for delaying his plans, but the Warmaster sought to turn the delay into a victory and was obliged to reinforce the Iron Warriors with troops from the Sons of Horus, the Alpha Legion, and the Emperor's Children. Fortunately, a contingent of Loyalists led by the nearby Battle-Captain Garro of the Death Guard escaped Isstvan III aboard the damaged Imperial frigate Eisenstein and fled to Terra to warn the Emperor that Horus had turned Traitor.
On Isstvan III, the remaining Loyalists, under the command of Captains Tarvitz, Garviel Loken and Tarik Torgaddon, another Loyalist member of the Sons of Horus, fought bravely against their own traitorous brethren. Yet, despite some early successes that delayed Horus' plans for three full months while the battle on Isstvan III played out, their cause was ultimately doomed by their lack of air support and Titan firepower. During the battle the Sons of Horus Captains Ezekyle Abaddon and Horus Aximand were sent to confront their former Mournival brothers, Loken and Torgaddon. Horus Aximand beheaded Torgaddon, but Abaddon failed to kill Loken when the building they were in collapsed. Loken survived and witnessed the final orbital bombardment of Isstvan III that ended the Loyalists' desperate defence, of which he would also survive and manage to escape off-world. To prove his worth and loyalty to Lord Commander Eidolon of the Emperor's Children -- and thus to his Primarch, Fulgrim -- Captain Lucius of the 13th Company of the Emperor's Children, the future Champion of Slaanesh known as Lucius the Eternal, turned against the Loyalists that he had fought beside because of his prior friendship with Saul Tarvitz. Lucius slew many of them personally, an act for which he was then accepted back into the Emperor's Children on the side of the Traitors. In the end, the Loyalists retreated to their last bastion of defense, only a few hundred of their number remaining. Finally, tired of the conflict, Horus ordered his men to withdraw, and then had the remains of the Choral City bombarded into dust for a final time from orbit.
==== Flight of the Eisenstein ====
Seventy Marines of the Death Guard Legion and the Imperial Saint Euphrati Keeler led by Battle-Captain Garro had commandeered the Imperial frigate Eisenstein and, evading the Traitor forces of Horus, were able to escape from the Isstvan System into the Immaterium, after being told what was happening on the planet. Battle-Captain Garro was leading his company which was assigned to Horus for the Isstvan III campaign. Garro's company was turned on like so many of their Loyalist Battle-Brothers from the other Legions. They had managed to escape but suffered heavy loses to the pursuing Alpha Legion. The Eisenstein was badly damaged by the Alpha Legion battleship Gamma Mu during its escape from Isstvan III and it was assaulted by undead minions. Unknown to all, the Alpha Legion in hopes to become the greatest Legion had pledged themselves to the Chaos God of Pestilence, Nurgle. This insatiable need for importance and now unrelenting hatred towards the Death Guard led to a endless pursuit from the surface up into space and constant assaults, including the first known Plague Marines of Nurgle while it was within the Immaterium. This assault by Warp entities forced the ship to make a crash emergence from the Warp. The repeated traumas left all of the frigate's astropaths dead, and its lone Navigator was mortally wounded. However, Garro managed to attract the attention of passing Loyalist starships by setting the vessel's Warp-Drives to self-destruct and ejecting them from the starship. Rogal Dorn's Imperial Fists Legion's massive mobile fortress-monastery Phalanx and the Legion's fleet had been becalmed in the Warp for some time due to the waxing power of the Ruinous Powers as the Heresy began, and his Navigators sensed the detonation of the Eisenstein's Warp-Drives. Charting an immediate course for the location of the detonation, Dorn met with Garro, who explained to him all that had happened with the Traitor Legions. Dorn was reluctant to believe Garro's tale, but overwhelming proof from a Remembrancer (journalist) named Mersadie Oliton who had escaped from Horus' flagship, the Vengeful Spirit, and Garro's dogged insistence finally convinced the Primarch. The Phalanx fortress set a course for Terra.
The fate of the Eisenstein's survivors is unknown. Sequestered on Luna in a tower belonging to the Sisters of Silence after their arrival in-system, Garro, the rest of his Death Guard, Captain Iacton Qruze of the Luna Wolves, and the warriors of the Silent Sisterhood faced one of the Death Guard Marines named Solun Decius who had succumbed to the temptations of the Chaos God Nurgle after being infected with one of the Lord of Plague's more virulent illnesses now known as Nurgle's Rot by the undead minions Nurgle had unleashed on the Eisenstein. Seeking to end his pain, Decius allowed himself to become possessed by a Lesser Daemon of Nurgle, a variant Plaguebearer called the Lord of the Flies, becoming the first of the Death Guard to fall to Nurgle. Afterwards, Garro and Captain Qruze were met by Malcador the Sigillite, leader of the Council of Terra and the Emperor's Regent, who informed them that the Emperor had need of people who were strong of will and as "inquisitive" as they. Malcador ordered Garro to begin to comb the galaxy for 7 other Astartes from both the Traitor and Loyalist Legions who with him would become the founding members of the Imperial Inquisition and the militant arm of its daemon-hunting Ordo Malleus -- the Grey Knights.
=== Preparations and Allegiances ===
Much of Horus' later success arose from the thorough groundwork he had laid before the opening shots of the Heresy were fired at Isstvan III. He had already swayed the Primarchs Perturabo and Alpharius Omegon, of the Iron Warriors and Alpha Legion Legions, respectively, to the side of Chaos because of their own various personal grudges against the Emperor. Fulgrim of the Emperor's Children had been lured to the side of the Warmaster by the promise of power and personal perfection that the Chaos Gods, especially Slaanesh, offered to him and his vain Astartes. Lorgar of the Word Bearers, who had been responsible for the nascent rebellion and Horus's own corruption by Chaos, was also with the Warmaster. Three of the most loyal Legions who could not be swayed to the side of Chaos, the Dark Angels, Blood Angels and Ultramarines and their Primarchs, were sent on missions by the Warmaster far from Terra and the Isstvan System. The Imperial Fists and White Scars were too close to Terra to be contacted without raising suspicion, though Horus believed -- mistakenly -- that the White Scars' Primarch Jaghatai Khan, would ultimately take his side. Shortly before the Drop Site Massacre on Isstvan V, Fulgrim also attempted to sway his friend Ferrus Manus of the Iron Hands Legion to Horus' cause by using many of the same inducements that had been offered to the Adeptus Mechanicus, with whom the Iron Hands were closely allied in both temperament and philosophy. This attempt failed, not completely though, and Fulgrim barely escaped with his life. Angered by the rebuff, Fulgrim promised he would deliver Manus' severed head to Horus in recompense, a promise he wasn't to keep. The Blood Angels were sent to the daemon-infested Signis Cluster and the Ultramarines to the world of Calth, where a large Word Bearers force, under First Captain Kor Phaeron, had massed to hold Roboute Guilliman's equally massive Legion in place while Horus made his play for Terra.
Of the other eventual Traitor Primarchs, Konrad Curze, the Night Haunter, was due to face disciplinary action from the Emperor which he did not believe he deserved; and the Loyalists that were soon to fall were none the wiser of their fate.
== The Drop Site Massacre ==
The Isstvan System’s third world, comfortably close enough to the sun to support human life, was now a virus-soaked mass grave marking the anger of Horus Lupercal. The world’s population was nothing more than contaminated ash scattered over lifeless continents, while the bones of their cities remained as blackened smears of burnt stone – a civilisation reduced to memory in a single day. The orbital bombardment from the Warmaster’s fleet, payloads of incendiary shells and virus-laden biological warfare pods, had seemingly spared nothing and no one anywhere in the world. Isstvan III lingered now in silent orbit around its sun, almost grand in the extent of its absolute devastation, serving as the scarred tombstone for the death of an empire.
Ringing Isstvan V was one of the largest fleets ever gathered in the history of the human species. Without a doubt, it was the most impressive coalition of Astartes vessels, with the scouts, cruisers, destroyers and command ships of six entire Legions. With a precision that required mass calculation, the fleets of six Astartes Legions hung in the skies above Isstvan V. Shuttles and gunships ferried between the heaviest cruisers, while the decks of every warship made ready to deploy their warriors in an unprecedented, unified planetfall. Horus, traitorous son of the Emperor, was making his stand on the surface. The Imperium of Man had sent six Legions to kill its wayward scion, little knowing two of them had already spat on their oaths of allegiance to the Throneworld.
Aboard the Fidelitas Lex, Lorgar's flagship played host to a gathering of rare significance. There were commanders from the Night Lords, those Alpha Legion that had penetrated Loyalist Ranks, Word Bearers as well as the Primarch of the Night Lords; the Nighthaunter. Lorgar strode to the centre of the gathering of Traitors. He then proceeded to impress upon the gathering of his sons, brothers and cousin Astartes of the importance of their cause, and of the significance this day would hold in history. The Word Bearers and their allies believed that the Imperium had failed them and by being flawed to its core, imperfect in its pursuit of a perfect culture, and in its weakness against the encroachment of xenos breeds that sought to twist humanity to alien ends. And it had failed them, most of all, by being founded upon lies. The Imperium was forged by a dangerous deceit, and had eroded them all by demanding they sacrifice truth on the altar of necessity. This was an empire, propagated by sin, that deserves to die. And here, on Isstvan V, they would begin the purge. From the ashes would rise the new kingdom of mankind: an Imperium of justice, faith and enlightenment. An Imperium heralded, commanded and protected by the avatars of the gods themselves. An empire strong enough to stand through a future of blood and fire. The Emperor believes them loyal. Their three Legions were ordered to Isstvan V on His misguided conviction alone. But their coalition here and now was the fruit of decades’ worth of planning. It was ordained, and brought about according to ancient prophecy. No more hiding in the shadows. No more manipulating fleet movements and falsifying expeditionary data. From this day forward, the Alpha Legion, the Word Bearers and the Night Lords would stand together – bloodied but unbowed beneath the flag of Warmaster Horus, the second Emperor. The true Emperor. First Captain Sevatar of the Night Lords Legion uttered, "Death to the False Emperor," becoming the first living soul to utter the words that would echo through the millennia. The curse was taken up by other voices, and soon it was being cried in full-throated roars.
"Death to the False Emperor! Death to the False Emperor! Death! Death! Death!"
Thousands of Drop Pods and Stormbirds were deployed for the initial assault. The first wave was under the overall command of the Primarch Lion El'Johnson and besides his own I Legion, the Iron Hands led by Ferrus Manus, the Salamanders led by Vulkan, and the Raven Guard under the command of their Primarch Corax joined him. Vulkan's Legion assaulted the left flank of the Traitors' battle line while Lion El'Johnson, Ferrus Manus, the Iron Hands and Dark Angels charged straight into the centre of the enemy lines. Meanwhile, Corax's Legion hit the right flank of the enemy's position. The odds were considered unequal for the initial assault; 300,000 Traitor Marines against 400,000 Loyalists. Horus was aware of the location of the Loyalists' chosen drop site and his troops fell upon the Loyalist Legions.
The battlefield of Isstvan V was a slaughterhouse of epic proportions. Treacherous warriors twisted by hatred fought their former brothers-in-arms in a conflict unparalleled in its bitterness. The mighty Titan war engines of the Machine God walked the planet’s surface and death followed in their wake. The blood of heroes and traitors flowed in rivers, and the hooded Hereteks Adepts of the Dark Mechanicum unleashed perversions of ancient technology stolen from the Auretian Technocracy to wreak bloody havoc amongst the Loyalists. All across the Urgall Depression, hundreds died with every passing second, the promise of inevitable death a pall of darkness that hung over every warrior. The Traitor forces held, but their line was bending beneath the fury of the first Loyalist assault. It would take only the smallest twists of fate for it to break. The forces on the surface had been embattled for almost three solar hours with no clear victor emerging. The Loyalists waited for their second wave of "allies" to make planetfall, believing they would be reinforced for their final advance. In truth, the Traitors all knew their parts to play in this performance. They were all aware of the blood they would shed to spare their species from what they believed to be its coming destruction, and install Horus as the new Master of Mankind.
Though the Dark Angels, Iron Hands, Raven Guard and Salamanders had managed to make a full combat drop and secured the drop site, known as the Urgall Depression, they did so at a heavy cost. Overwhelmed with rage, the headstrong Ferrus Manus disregarded the counsel of his brothers Corax and Vulkan and direct orders from the Lion and hurled himself against the fleeing rebels, seeking to bring Fulgrim to personal combat. His veteran troops -- comprising the majority of the X Legion's Terminators and Dreadnoughts -- followed. What had begun as a massed strike against the Traitors' position was rapidly turning into one of the largest engagements of the entire Great Crusade. All told, over 90,000 Astartes warriors clashed on the dusky plains of Isstvan V. For all the wrong reasons, this battle would go down in the annals of Imperial history as one of the most epic confrontations ever fought.
The Urgall Depression was churned to ruination beneath the boots and tank treads of countless thousands of Astartes warriors and their Legions' armour divisions. The loyal Primarchs could be found where the fighting was thickest: Lion El'Johnson of the Dark Angels, massacring through Traitorous lines with the Lion Sword held high and slick with blood; Corax of the Raven Guard, borne aloft on black wings bound to a fire-breathing Jump Pack; Ferrus Manus of the Iron Hands at the heart of the battlefield, his silver hands crushing any Traitors that came within reach, while he pursued and dragged back those who sought to withdraw; and lastly, Vulkan of the Salamanders, armoured in overlapping Artificer Armour, thunder clapping from his warhammer as it pounded into yielding ceramite armour, shattering it like porcelain.
The traitorous Primarchs slew in mirror image to their brothers: Perturabo as he swung and fired left and right, butchering all that fell before him; Fulgrim of the lamentably-named Emperor's Children, laughing as he deflected the clumsy sweeps of Iron Hands warriors, never stopping in his graceful movements for even a moment; Alpharius Omegon, who worked side by side in spearing and slaughtering everyone.
And Horus, Warmaster of the Imperium, the brightest star and greatest of the Emperor's sons. He stood watching the destruction while his Legions took to the field, their liege lord content in his fortress rising from the far edge of the ravine. Shielded and unseen by his brothers still waging war in the Emperor's name. At last, above this maelstrom of grinding ceramite, booming tank cannons and chattering bolters -- the gunships, Drop Pods and assault landers of the second wave burned through the atmosphere on screaming thrusters. The sky fell dark with the weak sun eclipsed by ten thousand avian shadows, and the cheering roar sent up by the Loyalists was loud enough to shake the air itself. The Traitors, the bloodied and battered Legions loyal to Horus, fell into a fighting withdrawal without hesitation.
The second wave of "Loyalist" Space Marine Legions descended upon the landing zone on the northern edge of the Urgall Depression. Hundreds of Stormbirds and Thunderhawks roared towards the surface, their armoured hulls gleaming as the power of another four Astartes Legions arrived on Isstvan V. Yet the Space Marine Legions of the reserve were no longer loyal to the Emperor, having already secretly sworn themselves to Chaos and the cause of Horus. The Night Lords of Konrad Curze, the Word Bearers of Lorgar Aurelian, and the "Loyalists" of the Alpha Legion of Alpharius that numbered half of the entire Legion represented a force equal to that which had first begun the assault on Isstvan V. The secret Traitor Legions mustered in the landing zone, armed and ready for battle, unbloodied and fresh.
Dragging their wounded and dead behind them, Corax and Vulkan led their forces back to the drop site to regroup and to allow the warriors of their recently arrived brother Primarchs of the second wave a measure of the glory in defeating Horus. Though they voxed hails requesting medical aid and supply, the line of Astartes atop the northern ridge remained grimly silent as the exhausted warriors of the Raven Guard and Salamanders came to within a hundred metres of their allies. It was then that Horus revealed his perfidy and sprung his lethal trap. Inside the black fortress where Horus had made his lair, a lone flare shot skyward, exploding in a hellish red glow that lit the battlefield below. The fire of betrayal roared from the barrels of a thousand guns, as the second wave of Astartes revealed where their true loyalties now lay. Ferrus Manus looked on in stunned horror as Fulgrim laughed at the look on his brother's face as the forces of his "allies" opened fire upon the Salamanders and Raven Guard, killing hundreds in the fury of the first few moments, hundreds more in the seconds following, as volley after volley of Bolter fire and missiles scythed through their unsuspecting ranks. Even as terrifying carnage was being wreaked upon the Loyalists below, the retreating forces of the Warmaster turned and brought their weapons to bear on the enemy warriors within their midst. Hundreds of Iron Warriors, Sons of Horus and the Alpha Legion fell upon the veteran companies of the Iron Hands, and though the warriors of the X Legion continued to fight gallantly and had the support of the Dark Angels, they were hopelessly outnumbered and would soon be hacked to pieces.
The Raven Guard front ranks went down as if scythed, harvested in a spilling line of detonating bolter shells, shattered armour and puffs of bloody mist. Black-armoured Astartes tumbled to their hands and knees, only to be cut down by the sustained volley, finishing those who fell beneath the initial storm of head- and chest-shots. Seconds after the first chatter of bolters, beams of achingly bright laser slashed from behind the Word Bearers as the cannon mounts of Land Raiders, Predators and defensive bastion turrets gouged through the Raven Guard and the ground they stood upon. The Word Bearers kept reloading, opening fire again, hurling grenades and prepared to fall back. The Word Bearers Legion had taken up landing positions on the west of the field, ready to sweep down and engage the Raven Guard from the flank.
The Raven Guard were confronted by the treacherous Word Bearers, with their Primarch Lorgar, the First Captain Kor Phaeron and the First Chaplain Erebus at their vanguard. The two Legions fought one another in bitter combat. In the midst of this battle, the Word Bearers unleashed the elite unit known as the Gal Vorbak -- Astartes who had allowed themselves to be possessed by daemons. They attacked the Raven Guard's Primarch en masse, but despite the advantage of their numbers, Corax's formidable abilities as a consummate warrior proved to be more than a match for the possessed Astartes, and he slew them with impunity. Seeing the slaughter of his most favoured sons, Lorgar intervened and prevented the death of the remaining Gal Vorbak Astartes. The two opposing Primarchs then duelled one another in close combat, and the Raven Guard's Primarch quickly gained the upper hand over his outmatched brother. Lorgar had always been more of a scholar than a warrior and Corax prepared to execute him for his betrayal of the Emperor. Lorgar was spared from execution by the intervention of the Night Lords' Primarch, Konrad Curze, at the last moment. The Night Haunter and the Raven fought a brutal melee. Curze quickly gained the upper hand over his battle-weary brother and prepared to slay him, but Corax managed to escape death by taking to the sky with his master-crafted Jump Pack.
Ferrus Manus turned to face Fulgrim, his teeth bared with the volcanic fury of his homeworld of Medusa. The two Primarchs leapt at one anther, Ferrus wielding Fireblade and Fulgrim holding Forgebreaker. Their weapons had been forged in brotherhood, but were now wielded in vengeance, meeting in a blazing plume of energy. The two Primarchs traded blows with their monstrously powerful weapons. Ferrus Manus wielded his flaming blade in fiery slashes, his every blow defeated by the ebony hafted hammer now wielded by his brother that he had once borne in countless campaigns. Both warriors fought with the hatred only brothers divided could muster, their armour dented, torn and blackened by their fury.
The two Primarchs traded terrible blows, wounding one another deeply during their fierce struggle. As Ferrus pushed himself to his feet and staggered towards the wounded Fulgrim, he cried out as he brought the flaming blade towards his brother's neck. But Fulgrim lashed out as he drew the single-edged, daemonically-possessed sword he had taken from the Laer temple dedicated to Slaanesh on Laeran and blocked the descending weapon. With the power of Chaos streaming from the blade, diabolical strength flooded Fulgrim's limbs as he pushed against the power of Ferrus Manus, feeling his brother's surprise at his resistance.
Fulgrim managed to surge to his feet and lashed out, his silver blade biting deep into the breastplate of Ferrus' armour, and the Primarch of the Iron Hands cried out, falling to his knees once again. Fireblade slid from his grasp as he gasped in fierce agony. As Fulgrim raised the silver sword in preparation to deliver the coup de grace to Ferrus Manus, he found that he did not possess the fortitude to deliver the killing blow. In an instant he saw what he had become and what monstrous betrayal he had allowed himself to be a willing party to. Fulgrim knew in that eternal moment that he had made a terrible mistake in drawing the sword from the Temple of the Laer, and he fought to release the damnable blade that had brought him so low.
His grip was locked onto the weapon and even as he recognised how far he had fallen, he knew that he had come too far to stop, the realisation coupled with the knowledge that everything he had striven for had been a lie. As though moving in slow motion, Fulgrim saw Ferrus Manus reaching for his fallen sword, his fingers closing around the wire-wound grip, the flames leaping once more to the blade at its creator’s touch. Fulgrim’s blade seemed to move with a life of its own as he swung the blade of his own volition. Fulgrim tried desperately to pull the blow, but his muscles were no longer his own to control. The daemonic blade sliced through the genetically-enhanced flesh and bone of one of the Emperor's sons. The Iron Hands' Primarch fell to the ground, a huge gash across his body that almost severed him in two. Ferrus Manus twitched and convulsed on the ground and Fulgrim stared in disgust at what he had done. His moment of sadness was to soon be forgotten, as the Primarch of the I Legion set upon him in an onslaught of blows, and a blinding light engulfed the battlefield.
=== The Red Angel Descends ===
Whilst Lion El'Johnson set about taking revenge for the supposed death of Ferrus Manus of the Iron Lords, a great figure never seen before descended upon Isstvan V, leading an army of untold proportions. It was Angron, the Primarch of the XII Legion. None would recognise him however, as this was his first appearance ever.
Many decades prior, Angron had led an uprising on the world of Nuceria, the world on which he landed during the Scattering of the Primarchs. During the Rebellion, Angron was the only one to notice the fleet that appeared within the skies, and a vast Golden ship that dwarfed the rest, before the fleet disappeared in the blink of an eye. Some ten Terran years later, that same fleet and the same golden ship once again filled the skies above. This time, the inhabitants of the now united and conquering world looked up to see the fleet stay. Lord Angron, King of Nuceria, saw this and pondered. The nails which once bit into his brain had long since been removed, but he was still the same ruthless butcher he had once been, only difference was he now led a whole planet that he had united. When he realised those above wouldn't leave, he stepped down from his throne to greet them. He was met by a golden figure larger than him, who introduced himself as the Emperor of Mankind and his father. Angron was as enraged as he ever was as he listened to the Emperor speak. Why had he not saved him all those years ago? Soon a battle broke out between the King of Nuceria and the Emperor's Guard. They were all slain, and Angron along with his armies fled. Angron vowed this would be the last time he would ever retreat, as he watched his world be bombarded from orbit.
Angron and his armies ventured for decades, before settling on a planet that they would call Nuceria Primus. Situated in the Eye of Terror, the planet was held by Daemons of Khorne, and Angron led his armies in a ruthless purge of daemonic presence. Soon, Angron and his armies would've conquered many worlds, earning them the name, the World Eaters. Half way across the Galaxy, Sanguinius the Great Angel of the Blood Angels Legion led not only his own, but his brother's legion as well. The XII Legion, the War Hounds, would never be led by Angron.
On Isstvan V, it was the Nucerian 1st Army, the World Eaters, and four more that he led. Even though they faced a foe much larger than them, the mortals fought with great bravery. Angron had pleaded with Khorne to let him lead an army of daemons, but the Lord of Skulls made it clear that Angron was not to be the Champion of Khorne until he led a Legion of Adeptus Astartes. His brother, Konrad Curze of the Night Lords, took his place as the Champion of Khorne. So Angron descended as a he was when he led the Rebellion on Nuceria, slaughtering Astartes of the Raven Guard wherever he swung. His armies stood, killed and died by his side, but the Red Angel wasn't paying attention to it. Nor was he paying attention to his arch-enemy, the Nighthaunter. It was the duel between his two brothers, the Primarchs of the Dark Angels and the Emperor's Children that he watched whilst slaughtering those that stood in his axes' paths.
=== The New Traitor ===
Fulgrim was outmatched by the Lion, who attacked him with unrelenting fury. He was distracted by the death of his brother, Ferrus Manus, and was unprepared. The Lion ended the duel quickly, as he faked an attack to the head, sliced at his brother's legs then went of his head. The fake had thrown the great swordsmen off and the huge gash in his leg made Fulgrim drop to one knee. His blade wasn't raised in time to stop the Lion Sword from cutting clean through his neck. The head of the III Legion's Primarch rolled along the floor, and the sight shocked the now awakened Ferrus Manus. The blinding flash that consumed the world has been centred around Ferrus Manus. As he rose, his mind was flooded with new found strength, that of the Chaos God Tzeetch. The daemon blade that had cut him almost in two had allowed the Chaos Gods to get to him. Now Tzeetch had a Champion too. 
The new Traitor immediately charged the Primarch of the Dark Angels, picking up the hammer Forgebreaker and the sword Fireblade. The Iron Hands and Dark Angels were confused beyond belief as they witnessed the two Loyalist Primarchs battle. The Iron Hands were even more confused as the Emperor's Children stopped firing at them and instead turned all of their arms upon the Dark Angels. For moments the Iron Hands slaughtered the Emperor's Children unopposed, until a huge psychic wave washed over them. Within moments the Dark Angels were now being assaulted from two sides, and they fell like rain.
The Death Guard that had come to aid couldn't help, nor could the Imperial Fists. All that could be done was to evacuate. The Raven Guard and Salamanders were down to less than half number they started with. The Dark Angels were still strong in numbers, with them only taking large amounts of casualties within the dying embers of the battle. The Death Guard lost 3 whole casualties due to the presence of the Nurgle-infused Alpha Legion, including Brother-Captain Typhon. Aboard the ships that managed to leave the system were Salamanders, Raven Guard, Dark Angels. Loyalist Iron Hands, Loyalist Alpha Legion and Loyalist Iron Warriors. Aboard the Endurance, the flag-ship of Mortarion, an assembly was called of the surviving Primarchs and commanders. Primarchs Mortarion of the Death Guard and Rogal Dorn of the Imperial Fists were already present. First came Corvus Corax and the Raven Guard commanders. Then Loyalist Iron Hands and Iron Warriors. Then Vulkan and his surviving commanders of the Salamanders. Finally, Lion El'Johnson and the Dark Angels and Omegon and a handful of Alpha Legion commanders. Everyone drew arms and was ready to butcher the traitors, but the Lion calmed them all, explaining how Omegon and his troops that were untouched by Nurgle's Plague sought refuge with the Dark Angels. Once everyone was convinced of Omegon's absolute loyalty to the throne, an oath he never renounced, the plans for vengeance were made.