Where the populations of Eldar were greatest, the warp literally spilled through their minds and mixed with material space. This created the scattered zones of warp overlap in the material universe, the largest and most significant of which is the Eye of Terror.

The Emperor of Mankind had long forseen the creation of Slaanesh and had prepared for that fateful day. By the time that the warp storms were ended by the birth of Slaanesh, the Space Marines and other Imperial forces were ready to begin their reconquest of the galaxy. The forces of Chaos were already strong, and many human worlds had been taken over by Chaos Cultists or aliens. It was a long hard struggle, but with every victory the Imperium grew stronger as new warriors joined the Great Crusade.

Led by the Emperor himself and his mighty Primarchs the Great Crusade of mankind swept through the galaxy like a firestorm. Untold billions of humans on thousands of worlds were liberated by the triumphant Space Marine Legions. The dark and sinister hold of the gods of Chaos was shattered, alien domination was overthrown and he Imperium was forged in a heroic age of conquest and rediscovery. Humanity rose to the task of rebuilding its ancient heritage, and everywhere the alien oppressor was defeated and driven out. Chaos retreated to its own realms, to the zones of warp-real space overlap such as the Eye of Terror.


Pride and Betrayal


But the forces of Chaos were not quite so easily beaten. They whispered to the Primarchs from the warp, disturbing their dreams with promises of power, appealing to their pride, their martial prowess, and their courage. No single Primarch was wholly resistant to these unspoken temptations. The character of each was sorely tested, and fully half of them failed that test. So subtle was their temptation that they never even suspected how their own loyalities were changing.

For example, Mortation Primarch of the Death Guard Legion fully believed that he was the herald of a new age of justice, Angron of the World Eaters geneinely thought that he alone could save humanity from destruction. Horus too, the greatest Primarch of all, was convinced of the virtue of the martial ideals for which he fought.

By appealing to their virtue and courage, the Primarchs were tempted to lead their Space Marine Legions against the Emperor. Initially, even the Primarchs had little idea that they had fallen to Chaos, but when they rebelled their good intentions gradually fell away as Chaos saturated their souls. The Space Marine Legions that they lead also turned slowly but inevitably to Chaos. The corrupting influence of Chaos soon spread to the Imperial Guard and Adeptus Mechanicus forces, including the Titan Legions and the Legio Cybernetica. From there the rot spread further into the Imperium itself. Over half of the Adeptus Mechanicus alone were ready to join an Empire dedicated to Chaos.

The leader of the rebellion was the Warmaster Horus, the greatest and most trusted Primarch of all. He had stood by the Emperor's side throughout the long years of the Great Crusade. They had fought back-to-back at the siege of Reillis when the Emperor saved Horus's life. On the battlefield of Gorro, Horus had repaid the debt by hacking the arm from a frenzied Ork as it struggled to choke the Emperor's life out of him. The Emperor had entructed Horus with leading the crusades along the Eastern Fringe while he returned to Terra to consolidate the rule of the vast Imperium now under his control.

In the Emperor's absence Horus's plans were just coming to fruition when the Imperial commander of Istvaan III declared the whole of the Istvaan system an independent principality. The Emperor, ignorant of the change in the Warmaster, ordered Horus to pacify the system. Horus chose to do so by virus bombing Istvaan III from orbit. The voracious life-eater virus slew every living thing on Istvaan III in a matter of minutes; twelve billion souls died with a death scream that pulsed louder than the Astronomicon. Whole continents and hive cities were charred to ash as the mass of oxygen released by the instant rotting of all organic material on the planet burned in the atmosphere and covered the world in a gigantic firestorm which raged for days. Before the last fires were out Horus despatched the Titans of Legio Mortis onto the planet's surface to root out any who had survived in protective shelters or underground bunkers.

During the bombardment a handful of Space Marines still loyal to the Emperor seized control of the Frigate Eisenstein. They had discovered the taint of Chaos spreading through Horus's command and as the Warmaster withdrew to Istvaan V to mashal his forces the loyalists fled into warp space to warn the Imperium.


Outright Rebellion


Horus's fall came as a great shock to the Emperor. He hesitated, stunned by the extent of the Warmaster's treachery, unable to beleive that his friend and general was really gathering forces against him. The Inquisition began a purge of the Adeptus Mechanicus and Imperial Guard but fighting broke out almsot immediately as both organisations were shattered into loyalist and rebel factions. On Mars Tech-priests fought with ancient, forbidden weapons as both sides strove to win dominance.

The corrupted Imperium tore itself apart as old feuds were revived and ambitious planetary lords seized the opportunity to declare their independence or join with the Warmaster. Many of them did not realise what manner of monster they were allting themselves with but others embraced Chaos wholeheartedly. Planterary battles raged across the galaxy as rebels attacked loyalists or vice versa. The Imperial fleet dithered and only succeeded in driving the rebel ships from the Imperial home system. In the process they suffered such heavy casualties that they withdrew to their Luna bases.

After an almost fatal delay the Emperor finally ordered seven Legions of the Adeptus Astartes to destroy Horus and his rebels. Only with the death of Horus, the figurehead and inspiration of the rebellion, would the revolt come to an end. But organising and mobilising such a crusade to the other side of the galaxy took precious months. Horus used the time well, consolidating his position and establishing his claim as the "New Emperor" within hundreds of systems. Wherever Horus was accepted, the worship of Chaos followed.

The assault of the loyalist Legions against Horus's strongholds on Istvaan V were a disaster. The Legions struck with their customary ferocity and cunning but this time they fought brother Space Marines. Both sides possessed troops as fully capabale and hardened as the other, every stratagem and ploy was met and countered. In the end strategy was overturned by treachery as the initial wave of three loyalist Legions were first mauled during their landings and then destroyed in detail. Only five Space Marines, bearing the gene-seed of their departed brethern, eventually managed to escape and carry news of the disaster to the Emperor. Somehow Horus had managed to corrupt four of the seven Legions sent against him. After the initial landings the 'loyalist' follow-up waves had attacked their allies instead of the rebels.

Horus now controlled nine Space Marine Legions and had destroyed three loyal Legions. Throughout the Imperium loyalists and rebels were fighting each other to a virtual standstill, although the tide of battle was turning, ever so slowly in the Emperor's favour. Horus knew that if he could crush the heart of the Emperor's resistance he could remould the Imperium in his own warped image. He ordered an assault on Earth.


Total War


The real tragedy of the Horus Heresy was the ruination of the Emperor's finest creations - not only the Primarchs but the Space Marines as well. The rebel forces spread the corruption of Chaos everywhere they went.

Throughout the galaxy the forces of Chaos became stronger as humans were seduced by the values represented by the Chaos Powers and even to their worship. The Emperor's great spirit was weakened as the better qualities of humanity were perverted and misdirected by the subtle warping influence of Chaos.

Such was the position when the forces of Chaos gathered around Earth. The Luna bases, the bastion of Earth's defences, fell to Horus after a hard fight, and the rebel fleet moved into Earth orbit. After a brief battle the Terran defence lasers were quashed by heavy bombardment from space. The last squadrons of the loyal fighters poured volley after volley into the huge ships but failed to penetrate even their shields. Once their last shots had been fired the pilots steered the fighters directly into the enemy craft. It was a gesture of defiance - no more.

Horus's drop ships fell like rain upon the Imperial palace, disgorging company after company of Traitor Marines. The palace spread over many square miles of bastions, walls, corridors, sky-scraping towers, vast space ports and the fighting was fierce and determined. The Traitor Marines and rebel Imperial Guard units supported by Chaos Titans and huge daemonic engines gradually forced back the loyal Marines and Emperor's Guards.

The defenders refused to give way, and the attackers were forced to win their way foward step-by-step over the casualties of both sides. In places the dead lay so thickly that corridors were blocked by the press of bodies. Still the loyalists could not prevent the battle becoming a siege, and fighting raged along the walls of the outer palace for over a month. Eventually Titans of the Legio Mortis demolished parts of the towering walls and the Traitor Legions poured through to assault the inner palace.


The Emperor at Bay


As the rebel forces slowly closed the drawstring upon the loyalist troops, the Emperor readied himself for the final battle with his bodyguard of Space Marines and Custodes. Two of his Primarchs stood by him: Rogal Dorn of the Imperial Fists and Sanguinius of the Blood Angels. The last hour of humanity had come and the few gallant defenders prepared themselves for certain death. It was then, when his victory seemed certain, that Horus made his one and only mistake.

Horus lowered the defense shields on his orbitting battle barge. At the time it seemed that he wished to use a psychic probe to witness for himself the final moments of the Emperor. It was his undoing, for a soon as the shields fell the Emperor became aware of his presence. The Emperor did not miss this crucial opportunity. Within a matter of seconds the teleport links were keyed to Horus's barge and the Emperor, his immediate entourage and the two loyal Primarchs, Rogal Dorn and Sanguinius, were transported right into the nest of Horus himself.

Horus was the greatest of all Champions of Chaos, an Arch-Champion and Captain of the Great Powers - a Chaos Lord of the highest rank. As the Emperor and his band of warriors materalised inside Horus's battle barge they saw for the first time the full extent of the Primarch's treachery. The ship had been transformed into something so horrible that some of the Space Marines were sent instantly mad. Their minds were completely blasted by the sight, they gargled incoherently as they crawled and twisted on the deck. The faces of men and daemond leered at them from the bulkheads, they had not bodies, their flesh melted into the slimy black walls. With a disgusting sucking sound the creatures heaved themselves into the corridors, clawing and grabbing at the members of the boarding party.

It took only a few minutes to reach the bridge, though many brave men died in those minutes nd hordes of no-longer-human things perished amidst the flames and singing boltguns. There on the bridge the Emperor confronted his old Warmaster, only to discover Horus poised over the broken body of Sanguinius - the Primarch had found Horus first and had died at his hand.

The Emperor launched his attack, as much a struggle between two old friends as it was a struggle for the fate of humanity. Both knew that whichever of them won would inherit the rule of the galaxy and become the undisputed Emperor of Mankind. If Horus won then Chaos would reign supreme and mankind would join the Eldar as a long race.


The Golden Throne


The fight with Horus was waged both in the material universe and in the warp, their bodies and their spirits battling for survival. Though Horus dealt him grievous wounds the Emperor fought not only for his life but but of untold billions across the galaxy. It was Horus who faltered first, perhaps because some shred of humanity survived in the Primarch and betrayed him in the end. The Emperor destroyed his friend with the last vestiges of his strength, his body was all but destroyed, and his psychic powers were also dealt a severe blow.

With the death of the Warmaster the forces of Chaos on Earth melted away. Some of those not too long in the service of Chaos were suddenly free from its illusions and quickly switched sides, fighting with all the more vigour in their attempts to make amends for their treachery. Others whose corruption was more deeply rooted, seeing that all was lost, retreated to their ships and fled into open space. The Emperor's body was hastily returned to Earth and palced in a life-preserving stasis field.

The life support unit known as the Golden Throne was quickly built to encase the Emperor. His powers survived, but his body was shattered. At first he was able to communicate semi-coherently for brief periods; later he lapsed into complete silence. That silence has remained undisturbed now for almost ten thousand years.


Bitter Defeat


As news of the Warmaster's defeat spread out from ancient Terra loyalists attacked rebels with renewed vigour. Hard on the heels of the news came loyalist reinforcements and the tide of battle turned decisively against the rebels. The battles still raged on long and hard for a full seven years before the last rebel formations were destroyed or exiled.

Those rebels that could flee to the Eye of Terror did so. Many had declared for the Warmaster without comprehending that daemon worship was the rebellion's cause. They rapidly fell victim to the Traitor Legions, who, it is said, grew bored of the diet of human flesh.

With the future of the Imperium assured the Emperor passed judgement upon the rebels. They had broken faith with him and trafficked with daemons. They had become enemies of humanity and could not be suffered to live in the Imperium of Mankind. All record of the Traitor Legions would be expunged and they were to be driven into the dust nebulae and hell worlds of the Eye of Terror, banished from the material universe and obliterated from history. It would be as if the Traitor Legions had never existed.

In this decision the Emperor tempered his vengeance with reality - the Imperium was so weakened by its inner struggle that no other punishment was possible. But the Eye of Terror remains a dreadful canker in the heartwood of the Imperium, an open wound that drips corruption into surrounding systems and serves as a haven for deviants and heretics. Worst of all, the Traitor Legions still lurk in the Eye of Terror, consumed with hatred of the Emperor, The Imperium and all mankind.