Of the original thirty-two Legions of the Symaarian Imperium, fully twelve of them defected from the Emperor following his untimely demise. However, this is a story of the beginning of their betrayal, the extent of which was known to the wider Imperium only after the fact.
The Sons of Doom, who renamed themselves the Demogorgons, were ordered by their Warmaster Zheres Attila to deploy fully in the Tartarus System in the aftermath of the initial warp bombardments flooding out from the Dead Stars. This was a joint operation in conjunction with the entirety of the Legio Mortis, the Destroyers, and Praetorians Legions. On Tartarus V, these Legions converged on what Zheres Attila called a "nexus of corruption" that threatened the wider Imperium if it was not stopped. However, only a select few portions of these Legions were chosen to attack the planet's surface, which seemed odd at first. That no Warmaster would stand on the planet alongside their gene-children seemed strange, but the elected warriors did as they saw as a duty that would preserve the Imperium from further devastation.
True to Zheres' word, there was extensive cultist activity that had to be purged on Tartarus V. For five weeks, the combined efforts of the Legions fought and died for scraps of territory that culminated in a massive siege of the main stronghold of the cultist forces. Within a few days, the fortress was taken and the portals to another world were destroyed entirely. However, this was not the end of the battle, but merely its most humble beginnings.
The elements chosen to attack Tartarus V were selected not because of their long history of duty and service to the Imperium, but instead because they were still loyal to the Emperor. Zheres Attila saw fit to take his place in the Imperium as its leader after his father's death, and those who disagreed were deemed unworthy of his growing regime. Tartarus V was fired upon by Imperial ships, and those Legionaries who were still on the surface were caught in the blast radius of apocalyptic virus bombs that swept across the world in mere moments, erasing organic life where it remained in the cracks of civilization. Thousands of Legionaries lost their lives in little more than an hour, condemned to die because their loyalties remained in the dead Emperor.
Even after the virus died out, countless tons of necrotic gas haunted the atmosphere of Tartarus V. Thus, Zheres could have damned the galaxy to eternal civil war with a single spark. He did it with a plasma lance straight into the core of the planet, setting the entire planet aflame with temperatures that reduced architecture to smoking husks, and corpses into bleached bone.
Zheres Attila, however, did not anticipate that his plan would be found out by a Loyalist Legionary who yet stayed behind, part of the Praetorians Legion, who then managed to get into a ship and warn small pockets of Loyalist warriors on the surface of Tartarus V as well as a captain of the Legio Mortis aboard the flagship Grim Hand. This ship would return to Ferravius, home of the Doom Wolves, and last great bastion of the Imperium within the Primus Sector where Symaar Primus once hung in orbit around its humble star.
What resulted from this handful of Loyalist soldiers yet on Tartarus V was a brutal land war, as Warmaster Typhon of the Devourers could not hold back his brutal bloodlust any longer and boarded a Caestus Assault Ram along with a fleet of Devourers Legionaries and shot straight to the surface. Zheres, loathe to murder such a potent combatant with an orbital strike just to erase some Loyalist survivors, instead applied additional pressure by sending his newly-renamed Demogorgons into the fray as well. This combination of distractions, as well as the fact of the Grim Hand heading straight for a heavily fortified Imperial world, was enough to keep the Traitors from chasing after the rogue Legio Mortis craft and instead focus on wiping on the Loyalists on Tartarus V and then prepare for the inevitable counterattack from the remaining Loyalist Legions.
Meanwhile, on Tartarus V, the Praetorians Centurion-Captain who managed to warn his Loyalist brothers of the treachery in time, whose name has been remembered as Apollo Alumes, was named the de facto leader of the Loyalist resistance now facing an overwhelming Traitor offensive. Finding safety in the bombed-out fortresses they had laid siege to for over a standard month, the Loyalists held out against two remarkable surges of Traitor forces, having been able to funnel them into claustrophobic tunnels after collapsing the mountainside around the main entrance.
For several continued weeks, the Loyalists held strong against the land armies the Traitors continuously sent out against them, surviving only by scavenging armor and new weapons from their foes. Food, though a Legionary can sustain himself without nourishment for months on end, was nonexistent. If they were to fight for much longer, they would invariably starve or thirst to death with enough time. Eventually, however, that moment of despair would never come.
The Traitors finally managed to blast through the thousands of tons of debris the Loyalists blasted around the main entrance to the fortress, and the battle became increasingly desperate as Typhon led the final charge, bedecked in the polished skulls and helmets of fallen Loyalist warriors - including those of his own Legion. The Loyalists were outmatched, outgunned, and outnumbered. Cornered like rats, they fought nobly and desperately, but could not overcome their invaders and were slaughtered to a man.
Typhon returned to his flagship, the Executioner, with fresh trophies. As he had managed to stamp out the Loyalist resistance on the ground, Zheres had lost precious time and manpower in reinforcing Tartarus VII, a nearby world that would be the staging grounds for the next phase of his traitor movement. Though, it would be his masterpiece.
Kaligar Roxom, Warmaster of the Doom Wolves, received word of Tartarus V nearly five months after the battle itself had concluded, such were the trials of interstellar travel. He gathered to him Torquemada de Insanguinare of the Blood Acolytes, Severus Trajan of the Legio Ultra, Hephaestus Mann of the Fire Drakes, and Garnath Tyriere of the Angels of Vengeance, his most trusted brothers and fellow Warmasters of their respective Legions. They all agreed on a decisive beheading strike, a killing blow that would destroy the Traitor Warmasters and their Legions entirely. The chosen battlefield was Tartarus VII, and Kaligar would send Hephaestus, Garnath, Daxand Roth of the Legio Ferrus, Jaron Sigismund of the Soul Keepers, Tyros Dentor of the Crimson Bulwark, and Albion Corr of the Black Wings as a preliminary force to secure a landing zone. While they were doing that, a secondary wave of Legions commanded by Warmasters Argul Vandt of the Champions of Steel, Karvus Noct of the Knights of Terror, Tessai Khan of the Death Riders, Jezrahn of the Red Wake, Belecron of the Dark Prophets, and Eredon of the Legio Hydra were meant to fully crush the Traitors in one sweeping movement of unparalleled destruction.
Little did he or any of the Loyalist Warmasters know, but the secondary wave of Legions had already pledged their allegiance to Zheres Attila.
Tartarus VII was estimated to have been a decisive victory for the Loyalists. What they got was a massacre.
With the Praetorians, Demogorgons, Legio Mortis, and Devourers entrenched deep within the Gyastes Mountains on Tartarus VII, the first Loyalist wave were forced to push through miles of barbed wire and entrenched Traitor forces consisting of turncoat battalions of the Imperial Army as well as numbers of their own Traitor counterparts. With the weight of six full Legions as well as their Warmasters behind them, the landing force won the valley rather easily, pushing forward at a feverish pace and forcing the Traitors back into the mountains. Strangely, even the normally berserk Devourers as well as Typhon himself retreated from the fight. This was when the second wave was scheduled to arrive, and so they did, landing drop pods inside the deployment zone behind the initial wave.
But something was wrong, and Warmaster Lucius Tarnel of the Praetorians knew it. He had been longtime friends with Daxand Roth, his brother-Warmaster of the Legio Ferrus, and was loathe to see him on the opposite side of the battlefield. He knew the feeling to be mutual, but could not bear the bitterness between them knowing he had condemned those of his Legion still loyal to the Emperor to die on Tartarus V. With all speed, he sent hidden messages to several Legions of the second wave, notably Tessai Khan of the Death Riders, Jezrahn of the Red Wake, and Eredon of the Legio Hydra. His secret purpose behind these outgoing transmissions was for those Legions to hang back, and as those still knowledgable of Zheres Attila's orders moved forward to cut down the Loyalists, they would spring forward and catch the Traitors from behind. Little did Zheres Attila know, but these Warmasters had pledged their allegiance to Lucius and Lucius alone, and as the Warmaster of the Demogorgons issued forth the counterattack that signaled the Traitors to catch the first wave of Loyalists in a vice, the Praetorians purposely held back, waiting for the carnage to ensue as well as for the perfect moment to strike.
Confusion exploded amidst the ranks as those first Legions of Loyalist soldiers were caught up between two Traitor counter-offensives, receiving mixed messages from those loyal to Lucius Tarnel about their double-crossing of Zheres Attila. With these reinforcements in tow, however, the situation still looked bleak to the Loyalist forces, with them being outnumbered company-for-company. While the Loyalist Legions numbered ten to the Traitors' seven, those assembled under Zheres' banner were at full combat strength, including those just arriving to Tartarus VII. Out of the Loyalist Legions fighting, only the Red Wake and, incidentally, the Praetorians were at full combat strength, meaning the Loyalist Legions were outnumbered nearly 100-to-1. Yet the desperate message Lucius sent to his brothers Tessai Khan, Jezrahn, and Eredon was enough to at least muster a sizeable counter-counterattack.
What followed was absolute carnage. Armies meant to conquer star systems were confined to a battlefield measuring less than 100 square miles.
Massive armored columns rolled over fields of mangled corpses. Brother fought brother amidst blown-out tanks and fortifications, often using the bodies of their fallen comrades as cover. Imperial Army soldiers of both banners rampaged into enemy lines, only to find their unaugmented bodies proof of their own fragility, if anything. Bursts of blood and flesh highlighted the inferno, and the Warmasters of each Legion collided with hundreds of their gene-cousins at a time, becoming icons of death and terror.
Warmaster Garnath of the Angels of Vengeance made it his own personal vendetta to hunt down Karvus Noct of the Knights of Terror, a brother of his that he detested for his unsavory appetite for the skins and other bodily trophies from his victims. Long had Karvus mocked Garnath for his system of honor, something that Karvus spat on the second he sided with Zheres. Garnath could tolerate the insults to him, but never to his allies, and charged headlong into the ranks of the Knights of Terror, splitting heads and severing apart everything in the midnight blue armor of his hated sibling's Legion with sweeps of his greatsword. Of Karvus himself, he had an agenda with the Warmaster of the Black Wings: Albion Corr.
Meanwhile, somehow throughout the chaos of the colossal war, Daxand and Lucius became reunited and embraced, their brotherhood stronger than ever before despite Lucius' lapse in judgment. Without pause, they joined their Legions and fought in a noble harmony that none could overcome on the broad hillside of their chosen ground. Hephaestus Mann would forever remember the image of the two fighting back-to-back against a blood-red sky.
Tessai Khan and Eredon made it a point to harry the enemy force as much as possible, being more akin to fast attack Legions than the brutal grind of close-range and melee combat. Yet even this preference for war did not keep them from becoming uncharacteristically close to the enemy, often smashing through the lines on motorbike steeds and with passes of jetbike swarms that left bloody swaths cut out from heavy bolter and plasma cannon fire. But the predominant numbers of the Traitor forces belonged to the Demogorgons and the Champions of Steel, two Legions that were renowned for never succumbing to casualties no matter how severe. With their Warmasters on the field, this was doubly so.
Argul Vandt, infamous for bombarding Gothic City on Earth into a veritable wasteland, returned the kindnesses of his Loyalist brothers with each sweep of his deadly hammer, taking with it dozens of Loyalist lives.
Albion Corr and Karvus Noct came to fight on the steep slopes of the Slag Hills, near the westernmost edge of the battlefield. Though Karvus knew his brother well and their tactics were much the same, Albion Corr possessed with him more than a mere instinct for murder - he was a skilled combatant against all types, and his weapons were finely tuned to kill in a single blow rather than to cut and torture. Karvus was indeed hard-pressed to fight Albion, but he never once backed down, intent on not only defeating the Warmaster of the Black Wings, but to slice through his body slowly and painfully.
Garnath came upon their fighting too late, and Karvus took the momentary distraction to push Albion to the ground in an attempt to cut his throat. But the Warmaster of the Black Wings unfurled the wings of his jump pack and took to the skies, Karvus coming with him, and Garnath was left to his own anger as he threw down more Knights of Terror Legionaries, overcome with a feeling of uselessness.
But all of this was a mere precursor to the horror Belecron would unleash. His latent potential as a psyker, now no longer inhibited by the Emperor's law, grew into an overwhelming crescendo. Those Imperial Army battalions that arrived with him gladly gave up their lives to become the first "experiments" of the Warmaster of the Dark Prophet, turning their flesh into amalgamations of each other, the sum greater than the parts. These spawn of chaotic energies lumbered into Loyalist lines, throwing handfuls of Legionaries and regular soldiers alike as their strength outclassed even the mighty gene-enhanced warriors of the Imperium. Hundreds of these things prowled the battlefield, brought low only by a great expenditure of ammunition and determination in equal measures.
Seeing this, Garnath decidedly made a beeline for Belecron, an unexpected turn that the Warmaster of the Dark Prophets could not readily prepare for as he was tossed from his pedestal of flesh by Garnath's shoulder-charge. Before he could impale his brother, however, Garnath was tossed aside by Argul's warhammer landing squarely in his chestplate, stopping one of his hearts in the process. Argul would then wordlessly challenge the Warmaster of the Angels of Vengeance to a duel, aiming to permanently stop his brother's hearts with another strike of his weapon. Garnath evaded, and their battle commenced as all hell erupted around them.
Legio Hydra, Dark Prophets, Legio Mortis, the Red Wake, Seers of Vindictus, the Devourers, Legio Infernus, Knights of Terror, Death Riders, Champions of Steel, Praetorians