Masters of Forbidden Knowledge
The Thousand Sons Space Marine Legion
The Betrayal
The threat to the fledgling Imperium resolved by the council served to mask other, darker betrayals already in motion. On Davin, events were reaching their tragic climax as Horus, first among equals, Warmaster and right arm of the Emperor fell victim to the manipulations of Chaos. This threat would not be resolved by debate or decree. Enthralled completely by the dark powers, Horus emerged from the events on Davin intent on nothing less than the complete destruction of the Imperium. Suborning brother Primarchs and their Legions to join his own, Horus intended to take the rest of the Imperium, and indeed the Emperor himself, by complete surprise. He was a brillant strategist; he believed he had manipulated every possible factor to ensure his success. He had miscalculated in only one regard. Despite the decree of his Father and despite his own sworn promise, Magnus had not turned from the pursuit of the dark arts.
Seeing into the depths of the Warp from his sanctum upon Prospero, Magnus behld a vision of Horus' pledge of fealty to Chaos upon the fields of the feral world of Davin. Horus' treachery was revealed, every detail made known with total clarity. Magnus saw the too-human foibles of Fulgrim of the Emperor's Children and Angron of the World Eaters played upon masterfully by Horus, and greater forces veiled by the Warp. He saw the terrible trap being laid for Ferrus Manus of the Iron Hands, Vulkan of the Salamanders and cautious Corax of the Raven Guard on Istvaan V. He saw the Emperor's mightiest bastion of unalloyed loyalty, Guilliman's Ultramarines, being cleverly decoyed to the far side of the galaxy, where they could play little part in the drama to unfold. Alone in the entire galaxy, more clearly than even Horus himself, Magnus was given to understand the events at hand. He saw it all and understood the events at hand. He saw it all and understoof each consequence and every role, except his own.
There are generals, tacticans and great military minds who say that had Magnus acted upon his knowledge and taken ship with his Thousand sons he could have changed the course of the Heresy. Others point out that the Warp is an imprecise place, and Magnus could not be sure he would arrive in time to prevent Horus's treachery. Instead of direct intervention, Magnus embarked upon a more perilous path. The Primarch had never accepted the Emperor's belief in the peril of sorcery, and had broken his oath to turn from the pursuit of such knowledge.
In his precognitive vision of the coming war, and the warning it provided, Magnus was certain he had found proof of the value of his studies. With the combined power of his fellow sorcerers he set about casting a spell across time and space. Breaching all the protective hexes and wards of the Imperial Palace on Terra, he projected his warning of impending revolution into the presence of the Emperor himself, naming Warmaster Horus as its chief architect.
It was to be his moment of triumph and vindication, the occassion of his self-righteous justification. Only the power of Magnus's sorcery had revealed the viper within. Surely the Emperor would at last see its value. Instead, the Emperor named Magnus's sorceries themselves as the viper. He judged Magnus's accusation of his brother Primarch heretical and his blatant deception evidence of the worst sort of oath breaking. Magnus's pursuit of forbidden knowledge was deemed tragic proof that he had fallen under the sway of the very power the Emperor had warned him against. The Emperor's worst fears for the soul of his cyclopean son had been realized.
The content of Magnus's warning was ignored completely. It is said the Emperor broke contact with such force that psychic wards throughout the Palace arced with lightning and shattered. At the Emperor's side stood Russ, quaking with barely-contained wrath at Magnus's actions. The Emperor turned to him, for he knew he could be counted upon to prosecute his next orders without restraint. He ordered the Space Wolves to be unleashed upon Magnus and the scholar-soldiers of Prospero.
Only those who witnessed those distant days will ever truly know what happened upon Prospero when the Space Wolves attacked, as extant accounts often contradict each other dramatically. The epic, 'Prospero's Lament', describes a lengthy orbital bombardment by the Space Wolves, followed by a systematic campaign across the planet that took many days and nights, with a death toll of horrific proportions on both sides. On the other hand, one of the Space Wolves' strongest oral accounts of the battle, 'The Edda of the Hammer', asserts the Space Wolves took the Thousand Sons completely by surprise. The Space Wolves fell upon the City of Light from above (as Magnus had, so many years before) and reduced it in one terrible, bloody night of violence and carnage. The single night of burning libraries, crashing towers and feral mayhem is a potent image and the action described in the Edda matches the popular image of the Space Wolves. But the Edda is often criticized; for how could a planet of sorcerers, able to see across time and space and into the future, be so completely surprised as to face destruction in the course of a single night? How indeed, unless the dark powers which granted them their visions did not mean for them to see? Prospero was the ultimate horror for the scholarly Thousand Sons, as Russ and his Space Wolves smashed their way through the sanctuary of the City of Light. Russ's warriors built pyres from Magnus's libraries of books, parchments and ancient texts, destroying artifacts unique in all the galaxy with a stroke of the chainsword. Though they differ in their specifics, most accounts suggest Magnus himself met Leman Russ in hand-to-hand combat, Primarch against Primarch, berserker against giant in the ruined heart of the City. 'The War of the Giants', committed to print by Inquisitor Bastalek Grim from Space Wolf oral tradition, describes the titanic duel that followed:
'Magnus the Red did take to the field of battle, causing the ravaged ground to liquefy 'neath his mighty stride. Russ charged boldly the crimson behemoth and did lift the Cyclops off the ground. The Wolf-King broke the back of the Cyclops, and the last Thousand Sons, seeing their Primarch broken and cast down, did turn and flee. But as Russ raised Frostblade Mjalnar to deliver the killing blow, Magnus spoke a word of power, and did sink away into the indescent ground'
In accounting what took place at the last, claims of what occurred on Prospero's final night contradict wildly. Somehow, in the City of Light's dying moments, Magnus cheated Russ of total victory, and in so doing, paid the very price the Emperor had warned him against all along.
Everything that mattered to him was burning to the ground, and Magnus turned to what he knew best to save it. Magnus was swept upon the currents of the Warp, and there he found the knowledge he sought. His sorcerers, his beloved Legion, all the precious knowledge they had accumulated within the silver spires of the City of Light could still be saved. He discovered the solution looking back at him, as if it had always been there, watching his way, and subtly changing him to its own purpose. He beheld sorcery incarnate, promising knowledge, power and salvation. But this time it was on its own terms. Magnus was no longer the master of the way as he had believed himself, but servant to it. It is said that even then Magnus hesitated, but as he thought back to his city, his works, his knowledge and brethren, reduced to fiery ruin at the command of his own father, he changed his allegiance for all time.
And in that instant, the City of Light, its silver towers and vast libraries and its Legion of Thousand Sons vanished from the face of Prospero, and the Imperium forever. When Magnus and his Thousand Sons were seen again, it was above Istvaan V, fighting alongside Horus. Magnus had become a Daemon Prince of the Chaos god Tzeentch, Lord of Sorcery, and Changer of Ways. The battle for their souls and their fate now so complete, it leaves one wondering whether it was ever truly in doubt. Taken from White Dwarf 266US