Changes

==HistoryOverview=====PreludeThe Isstvan Conspiracy===An Imperial Expedition had assembled at Over a year before the battle, [[Warmaster]] [[Isstvan systemHorus Lupercal]] consisting had [[Battle of elements Davin's Moon|fallen]] on the moon of [[Davin]] thanks to a conspiracy by the [[Sons Word Bearers]].{{Fn|3}} He immediately set about constructing a plan to overthrow the [[Emperor]]. Still posing as the loyal [[Warmaster]] of the Throne of [[Terra]], Horusweaved a web of deceit and betrayal in preparation for open rebellion. This included sending Primarchs deemed likely to remain loyal such as [[Lion El'Jonson]], [[World EatersRoboute Guilliman]], and [[Death GuardSanguinius]] to the fringes of the Imperium to ensure they could not interfere with what was about to transpire. Meanwhile, he assembled those Legions whose Primarchs he had managed to turn to his cause: [[Fulgrim]] and a contingent of the [[Emperor's Children]]. Overall, over 200[[Angron]] and the [[World Eaters]], and [[Mortarion]] of the [[Death Guard]],000 Astartes were assembled for planning to use the operationcoming battle as a way to purge this force of remaining loyalist elements.{{Fn|1a}}

So it was that some 200,000 Astartes assembled in the [[Isstvan System]], ostensibly to counter an anti-Imperial rebellion on [[Isstvan III]]. The Death Guard [[Space Marine Legion|Legion]] had received a distress signal from the former [[Imperium]] world of [[Isstvan III]] which stated that the colony had turned away from the [[Imperial Truth]] and that the former [[Planetary Governor|governor]], [[Vardus Praal]], was leading the rebellion. The assembled Imperial expedition was tasked with eliminating this threat. Initial skirmishes While Mortarion and Angron were fought on the outer system world of able to rendezvous with Horus at Isstvan III, Fulgrim was dispatched to potentially turn [[Isstvan ExtremisFerrus Manus]] where to the traitor cause and the Emperor's Children and Death Guard had managed to eliminate the enemy outpost. With the enemy forces blinded, Warmaster Horus brought about the Legions to hammer the rebel forcesat Isstvan were commanded by [[Lord Commander]] [[Eidolon]].{{Fn|1a}}{{Fn|1b}}

A combined assault was assembled by the Legions which invaded the planet determined to remove the threat of Initial skirmishes were fought on the rebels. Due to incorrectly mapped locations, many outer system world of the [[drop podIsstvan Extremis]]s that crashed at [[Choral City]] slammed into where the cityEmperor's towers which caused a delay in reinforcements as they were pinned in inaccessible locations. The [[Titan]] ''[[Dies Irae]]'' was also present at the planet Children and made use of its mighty weapons Death Guard had managed to eliminate heavy the enemy outpost. With the enemy positionsforces blinded, Warmaster Horus brought about the Legions to hammer the rebel forces.{{Fn|2c1a}}{{Fn|1b}}

Hundreds of Isstvanian soldiers had assembled to fight However, Isstvan III would be no easy conquest. The world was heavily defended against the threat of the Imperials. Though they lacked the genetically engineered nature of the Space Marinesany outside incursion, they defiantly fought against them with some succumbing to the unique weapon of the Isstvanians. A more dangerous threat to the invading Astartes were and the rebels possessed powerful [[Psyker]]-warriors dubbed [[WarsingersWarsinger]] among the rebels which managed to kill dozens of Space Mariness.{{Fn|2c1g}} Vardus Praal himself So it was killed by the Emperorthat a massive [[Drop Pod]] assault was launched onto Isstvan III's surface. Four primary targets were chosen for this attack at Isstvan's Children Astartes capital dubbed the [[Lucius (Choral City]]. The Emperor's Children)|Lucius]]would land at the Precentor Palace where the traitorous governor was believed to be, the World Eaters at the central plaza, and the Death Guard at the outer bunker network. The final and most difficult target would fall to the Sons of Horus, which would land east of the city at a vast ancient complex dubbed the Siren Hold. It was here that the most Warsingers were believed to be based.{{Fn|2d1g}}

===HorusThe first wave of Drop Pods fell upon the Choral City like hammer blows, landing after a brief but intense orbital bombardment. The first to land were the World Eaters at the city surrounding Precentor's Betrayal===With those squads Palace, who smashed into the central plaza and killed everything in their leaders that were known to be completely loyal to path. While quickly capturing the Emperor on plaza, the planet, battle for the Warmaster finally decided Precentor Palace would prove far more difficult due to initiate his planits heavy defenses which had been designed by Imperial military architects. A number of starships had secretly prepared It was here that the Emperor's Children next landed, using [[Life EaterDreadnought]] virus for deployment onto the planet. A signal was sent by Horus, who informed his loyal troops (such as the s and [[PrincepsMelta Gun]] of the ''Dies Irae'') of the attack, allowing them -armed infantry to seal all doors to prevent burst into the virus from infecting the crewpalace and fight their way through each level. After whichMeanwhile, the ships began Death Guard managed to fire onto quickly overrun the planet itself. The assembled western fortification line against half-insane [[RemembrancerMutant|mutated]] Order was present on the ''[[Vengeful SpiritImperial Army]]'' while this happenedrebels. After Horus declared his intentions of taking Led personally by Mortarion, the Death Guard quickly silenced the rebels [[Golden ThroneBasilisk]], his Astartes went about exterminating guns and [[Malcador (Tank)|Malcador]] heavy tanks before pushing through the Remembrancerstrench and bunker networks. The virus itself devoured and destroyed hundreds These assets were given heavy air support alongside a compliment of Astartes on the planet as their armour afforded them no protection from the deadly bio-weapon[[Legio Mortis]].{{Fn|1g}} Due to incorrectly mapped locations, with even many of the rebelling Isstvanians dying in [[drop pod]]s that crashed at [[Choral City]] slammed into the genocidal attack. All that was left was a sludge of dead organic matter after city's towers which caused a single blast delay in reinforcements as they were pinned in inaccessible locations. The [[Titan]] ''[[Dies Irae]]'' was directed also present at the planet which created a firestorm which scorched the world leaving it a dark dead planetand made use of its mighty weapons to eliminate heavy enemy positions.{{Fn|2a2c}}

Despite his carefully laid planAt the Siren Hold, the loyal Sons of Horus landed in a labyrinth of lesser shrines, arches, and walkways. The Sons of Horus were quickly scattered amidst this ocean-like edifice and came under heavy fire.{{Fn|1g}}A more dangerous threat to the invading Astartes were not eliminated the Warsingers which managed to kill dozens of Space Marines each with their sonic songs.{{Fn|2c}} It was at this point in the battle that an enormous scream erupted across the Choral City and beyond, driving the people of Isstvan III into uncontrolled hatred and madness and driving them to resist the Imperials by any means necessary. All four Space Marline Legions now had to contend with waves of frenzied civilians in addition to the standard rebel troops.{{Fn|1g}} At the Precentor Palace, the Emperor's Children advanced room by room at significant cost thanks to the presence of many Warsingers. There were also large numbers of a previously unencountered type of rebel elite. These warriors were surgically modified and mutilated, clad in black vitrified armor, and wielding strange weapons that spat killing blasts of sound or darts of liquid metal. However they eventually were warned able to fight their way to the throneroom, where Captain [[Lucius (Emperor's Children)|Lucius]] slew the heavily augmented Vardus Praal personally.{{Fn|1h}}{{Fn|2d}} Simultaneously deep within the Siren's Hold Tomb Spires the Sons of Horus under the betrayal by command of [[Garviel Loken]] fought into a strange corpse-filled shrine and slew many Warsingers before destroying the complex. These two acts managed to dispel the strange cacophony that held sway over the Choral City, and within hours the rebellion was smashed. Quickly securing their remaining objectives, the victorious Space Marine CaptainMarines celebrated their hard-won victory, unaware that disaster was about to strike.{{Fn|1h}} ===Betrayal===With those squads and their leaders that were known to be completely loyal to the Emperor on the planet, the Warmaster finally decided to initiate his plan. All communication with the orbiting fleet ceased and the Titans of the Legio Mortis went silent as they sealed themselves against biological threats.{{Fn|1h}} The warships ''[[Vengeful Spirit]]'', ''[[Firebird (Battleship)|CaptainFirebird]]'', ''[[Andronius]]'', ''[[Killing Star]]'', ''[[Indomitable Will]]'', ''[[Gauntlet of Spite]]'', ''[[Warchild]]'', ''[[Eisenstein]] ''{{Fn|4a}}, and ''[[Saul TarvitzConqueror (Ship)|Conqueror]] '' all lowered into low orbit and launched salvos of [[Virus Bomb]]s upon the Isstvan III's surface.{{Fn|1h}} The assembled [[Remembrancer]] Order was present on the ''Vengeful Spirit'' while this happened. After Horus declared his intentions of overthrowing the Emperor, his Astartes went about exterminating the Remembrancers.{{Fn|2a}}  Each virus bomb contained thousands of submunitions, each of which contained deadly [[Life-Eater Virus]]. These sub-warheads detonated in the lower atmosphere and rapidly spreading the phage across the surface. The Life-Eater was one of the most insidious and terrible weapons forged by Mankind, and every piece of organic matter it encountered rotted into liquid refuse within seconds. Billions of Isstvanians died in agony alongside all of the planets flora and fauna. Even the oceans turned into a greenish sludge as all organic matter within rotted away. But the destruction was not over yet. The Life-Eater was intentionally designed so that the miasma caused by its victims transformed into a highly flammable gaseous sludge. At Horus' command, a single [[Lance]] strike was launched from orbit, detonating this toxic stew and engulfing the planet in a tsunami-like firestorm. The resulting inferno engulfed the entire surface of Isstvan III, incinerating its now-empty cities. All that remained of Isstvan III in the afterlife was a dark dead planet.{{Fn|1h}} Meanwhile in orbit, many vessels fell into anarchy as loyalist elements resisted the unfolding treachery. The [[Torpedo]]-monitor ''Ducroix'' turned its guns upon the traitor armada before being torn apart by retaliatory fire. The [[Heavy Cruiser]] ''Sunstone'' was the site of an intense battle between loyalist and traitors who fought each other on every deck, eventually suffering a reactor meltdown and exploding. The [[Mechanicum]] [[Ordo Reductor]] War Galley ''[[Xerxes 9-7-7]]'' refused an order to surrender to Horus and was shot down onto Isstvan III's Childrensurface.{{Fn|1i}} Surprisingly, elements within the vessel survived the crash and fought alongside the loyalists under [[Magos Reductor]] [[Calleb Decima]] Legion. This consisted {{Fn|1m}} But even before the first Virus Bombs had been launched, Horus' plan had already begun to unravel. Unknown to him, several loyalist officers within the armada had learned of the treachery and managed to warn the Space Marines on the surface. Chief among these were [[Nathaniel Garro]] of the Death Guard and [[Saul Tarvitz]] of elements the Emperor's Children. Warned of the World Eatersimpending disaster, some 90, 000 the Sons of Horus, World Eaters, Death Guard , and Emperor's Children who on the surface managed to find bunkers or other sealed locations seal themselves away inside the remaining bunker and catacomb networks on Isstvan III. Thanks to the warnings given by Garro and Tarvitz, some 2/3rds managed to survive the firestormbombardment, though most of the accompanying Imperial Army, [[Mechanicum]] troops, and [[Administratum]] functionaries were not so lucky. Once this Meanwhile, Garro was over, they began able to take stock wrest control of their position. Horus himself was outraged, not only at this but that the ''[[AngronEisenstein]] '' with his loyalist Death Guard and escape the Isstvan System for a perilous journey to [[PrimarchTerra]] to warn of the World Eaters treachery.{{Fn|1i}} While most of the Astartes had survived in their shelters, a shock fell over them. Never before had such a terrible betrayal befallen the Legiones Astartes, and worse still their own Primarchs had landed on Isstvan III without permission disowned them. This shock soon turned into righteous defiance, and attempted the remaining survivors pledged to fight against to the remaining loyalistslast and not go down silently. This forced {{Fn|1b}} But before Horus could formulate a new plan, the maddened [[Angron]] unexpectedly descended from the Warmaster's hand 'Conqueror'' to fight against the surviving Astartes Isstvan III with 50 companies of frenzied World Eaters, intent on massacring the planet in order not to show weakness to loyalists. The recklessness and insubordination infuriated Horus, who no longer could simply annihilate Isstvan from orbit without eliminating a key commander for his brothers and that he was committed to the goalcoming wider rebellion.{{Fn|2a1b}}

Seeing that they were betrayed, Captains [[Garviel Loken]] and [[Tarik Torgaddon]] of the Sons declared to the surviving Astartes of the XVI Legion that they were once again the Luna Wolves and marched to Praal's stronghold, where they dug in with the surviving members of the Emperor's Children under Saul Tarvitz and [[Lord Commander]] [[Abdemon]]{{Fn|1j}} and combated against the traitor forces. While bringing about grievous casualties {{Fn|2e}} The loyalist World Eaters fell under the command of Captain [[Ehrlen]] and [[Centurion (Rank)|Centurion]] [[Shabran Darr]]{{Fn|1k}} while the Death Guard survivors were led by [[Crysos Morturg]]. The loyalists pledged to make their traitorous brothers pay for every inch of ground.{{Fn|1h}}  The first ground combat between loyalist and traitor saw Angron and his berserkers charge headlong into a bunker complex defended by some 2,000 loyal World Eaters under Ehrlen. Both sides succumbed to Horustheir [[Butcher's Nails]] and the battle soon erupted into a chaotic melee. During the fighting, Ehrlen was overcome by dozens of his former brothers and torn apart.{{Fn|1b}}{{Fn|1l}} Nearby in the remains of the Choral City plaza, 7,000 World Eaters butchered one another in a frenzy of violence. But Angron was an avatar of carnage, and the Primarch's forcespresence allowed the Traitors to emerge victorious at unexpectedly heavy cost. Perhaps surprisingly, Angron seemed pleased with the defenders were dwindling rapidly due contest that had erupted and is said to have yelled "It is well done!" before moving on in search of new foes to their limited numbersbutcher. They {{Fn|1l}} With destroying Isstvan from orbit no longer an option and knowing Angron needed support against the surviving loyalists, Horus had hoped no choice but to bring about a high number launch his armies back upon the surface of casualties Isstvan III for a protracted struggle. The Emperor's Children under Eidolon were the Warmaster and next to delay himdeploy, thus giving landing near the scorched remains of the Precentor Palace and meeting fierce resistance from Tarvitz's loyalist Emperor's loyal forces time Children. Instead of finding confused survivors, the traitors encountered skilled and determined resistance and were forced to reach the Isstvan systemretreat, leaving dozens of damaged or destroyed vehicles in their wake. The rechristened Luna Wolves under Loken and Torgaddon launched a series of successful hit-and-run ambushes that decimated their traitorous brothers. They managed {{Fn|1m}} The traitors next tried to repel wave after wave led by various commanders such use their air superiority to their advantage, but gunships and aircraft were vulnerable to ground fire and many loyalists would simply wait in hiding for them to pass on. Remaining loyalists were present even in the traitor fleet, as demonstrated when the Sons of Horus [[Lord CommanderStrike Cruiser]] ''Minotaur'' was destroyed when a [[Storm Eagle]] unleashed its payload inside its hangar bay, its crew broadcasting "avenger the blood of Terra!" before choosing suicide over treachery. While Horus had succeeded in the initial phase of his plan to separate his traitorous Legions from their loyalist elements, the entire campaign soon spiraled into a disaster.{{Fn|1l}} In the ensuing months of bitter fighting, the defenders made the traitors pay for every piece of ground gained. Eidolon (launched multiple attacks upon the Precentor Palace but each time was beaten back by Tarvitz and his Emperor's Children)|Eidolon. The [[Venerable Dreadnought]] [[Rylanor]] who fought alongside Tarvitz, gaining infamy in the battles. Many times Rylanor was thought destroyed, only to always rise again and reap carnage upon the enemy.{{Fn|1m}} In one engagement, Eidolon forced to scurry away after the loss of his [[Chaplain]] [[Charmosian]].{{Fn|2e}} Meanwhile, Loken and Torgaddon continued their strategy of mobile defence, proving too elusive to encircle and pin down. Roving bands of loyal World Eaters continued to harry the traitors, and to the northwest the loyal Death Guard stubbornly fought on in an intact bunker network.{{Fn|1m}}  However despite the determined and skillful loyalist resistance, their foes were too many and too well-supported by heavy armor, air power, and Titans of the Legio Mortis. It was only a matter of time before they were dwindled down to nothing by sheer attrition. The defending loyalists were well aware of this reality and had no delusions of surviving the coming struggle, but this did nothing to shake their determination to resist their foes. The only advantage that the loyalist could take advantage of was the eruption of violent storms across Isstvan III that were brought on by its destruction. These storms served to further delay the traitor advance.{{Fn|1l}} By two months into the conflict some 10,000 loyalists were believed dead, but they had inflicted twice that upon the traitors.{{Fn|1m}}

It was believed that they would have been capable The first cracks in the loyalist defense came from the Death Guard in the northwest of holding out the Traitor forces for some timeChoral City, who were faced with the most desperate situation as both Angron and Mortarion each advanced on their position. HoweverAlready hammered by the vicious frontal assault of the World Eaters, Mortarion landed his great relic assault ship ''[[Lucius (Emperor's Children)|LuciusOmen]] had grown '' and used its turrets to despise Saul Tarvitz sweep the ground clear of trenches and wanted to rejoin his Legionpillboxes. Using a slain In their wake came heavy [[ChaplainSpartan Assault Tank|Spartan]]'s helmet communicator, he contacted Lord Commander Eidolon [[Fellblade]]s and arranged for the betrayal of his comrades[[Typhon Heavy Siege Tank|Typhon]] tanks with Mortarion personally leading them. Lucius himself had slain all the defenders at that part of the encampment promising Eidolon not only glory One by defeating the loyalists but giving him the head of Saul Tarvitz. Despite his boastone, Lucius was defeated when Tarvitz had reinforcements, forcing Lucius to flee back to the Emperor's Children Legionloyalist defensive bastions were subdued.{{Fn|2f1m}}

The defenders were now too few Nearly two months into the fight, the last of the great storms began to wane and a the loyalist situation rapidly worsened. Tarvitz and Horushis Emperor's Children still held the Precentor's patience had dropped to Palace and the point that he ordered Luna Wolves still held the Siren's Hold, but in the northwest the loyal Death Guard were finally smashed by Mortarion and Angron'Dies Iraes onslaught. In a confusing battle dubbed the "Veil of Grief", the legendary discipline of the Death Guard broke down as some surviving loyal elements within Mortarion'' to destroy s own armies turned their guns upon their traitorous brothers or the loyalist fortificationsWorld Eaters. Many more were Traitor and Loyalist became lost in the maelstrom, with Death Guard Marshal [[Durak Rask]] being killed by [[Crysos Morturg]]. Mortarion himself is said to have been wounded in this action leaving the battle, burned by plasma fire from one of his own [[Predator]] tanks before he and his [[Deathshroud]] hacked it to pieces. The respite the confusion brought allowed some of the surviving loyal Death Guard to withdraw. In the aftermath a small band spiteful Mortarion used the waning storms to land massive amounts of survivorsreinforcements and poured heavy armor and Titans into the area, annihilating what resistance they still encountered. The loyalist Death Guard did not give up however, and withdrew to subterranean bunker and catacomb networks to continue to fight on. Mortarion had expected this however, and brought in [[Vortex Weapon|Vortex charges]] and [[Hades Breaching Drill]]s to clear out these remaining bastions.{{Fn|1m}} Meanwhile at the Choral City, Horus unleashed [[Abaddon]] and his elite [[Justaerin]] to the southwest. With great reluctanceBacked by heavy armor, airpower, newly christened [[Dark Mechanicum]] troops, and Titans, Angron they flushed out and wiped out what resistance was recalled by encountered. Shockingly, the Warmaster as traitorous Sons of Horus were accompanied by the other Traitor forces witch-priests of [[Davin]]'s [[Serpent Lodge]], who returned used the power of the Warp to their shipsunleashed a sickening shroud across the battlefield. This {{Fn|1m}}  Eidolon launched another assault on the Precentor's Palace, this time, Horus planned backed up by freshly landed Titans of the Legio Mortis and [[Legio Audax]].{{Fn|1n}} Formerly loyalist Captain [[Lucius (Emperor's Children)|Lucius]] had grown to despise Saul Tarvitz and wanted to finish off rejoin his enemies once Legion. Using a slain [[Chaplain]]'s helmet communicator, he contacted Lord Commander Eidolon and arranged for the betrayal of his comrades. Lucius himself had slain allthe defenders at that part of the encampment promising Eidolon not only glory by defeating the loyalists but giving him the head of Saul Tarvitz. He commanded Despite his boast, Lucius was defeated when Tarvitz had reinforcements, forcing Lucius to flee back to the great ships Emperor's Children Legion.{{Fn|2f}} Meanwhile, the traitor Titans combined their fire on part of the structures wall, finally blowing a hole in orbit the structure and allowing them to begin bombarding advance inside for the first time. The first into the planet which killed breach however was not the traitorous Emperor's Children however, but Angron and his World Eaters who massacred any remaining defenders which included loyalists encountered inside.{{Fn|1n}} To the northwest at the Siren's Hold, Abaddon's Justaerin came into contact with Loken and Torgaddon's Luna Wolves after landing via [[Caestus Assault Ram]]s.{{Fn|1n}} Backed by gunships and heavy armor, Abaddon's [[Terminator]] elite were finally able to break their way into the Siren's Hold. Hopelessly outnumbered and outgunned, the Luna Wolves fought to the last but the Siren Hold fell within the fatally wounded Garviel hour.{{Fn|1n}} Despite a valiant final battle against Abaddon and [[Horus Aximand]], Torgaddon was slain and Lokenwas buried under rubble from a Titan's blast.{{fnFn|2b}} The traitors unleashed [[Phosphex]] into the lower catacombs, burning those who remained below alive as Davinite Priests used their dark arts to identify any living who remained. By now, the war had devolved into a hunt for the small pockets of remaining loyalists who were all eliminated to a man.{{Fn|1n}} \ There were ultimately only handful of loyalist survivors, such as Loken,{{Fn|5}} Morturg,{{Fn|6}} and Rylanor, who unknown to all sides remained hidden on the planet for millennia after.{{Fn|7}}

Once ===Aftermath===While victorious, the purge battle had proven far more costly and time-consuming than Horus could have envisioned. Moreover, by this point [[Fulgrim]] had finally returned with troubling news. Ferrus Manus had refused to join their cause and it was only a matter of time before their treachery was discovered by Terra. Horus finally withdrew his Legions was completeforces from Isstvan III, Horus began preparations leaving an utterly dead world behind. He immediately set about for the next phase of his reformulated plan, regaining the initiative with an [[Drop Site Massacre|next stageeven greater act of treachery]] of the Horus Heresy at [[Isstvan V]].{{fnFn|1n}}{{Fn|2b}}