Siege of Terra - Endgame: The siege of Terra following the initial assault on the Imperial Palace lasted for 55 solar days. Both sides knew that the defeat of the Imperium of Man was near after the defence of the Eternity Gate.Sensing this, and knowing that he must complete the siege before the arrival of Loyalist reinforcements from the other Space Marine Legions that were already on their way, Horus prepared to teleport to the surface from his flagship, the Vengeful Spirit, to lead his forces in person.Before this could happen, the Word Bearers' First Chaplain Erebus broke the news to Horus: their daemonic allies in the Warp had informed them that the Dark Angels and Space Wolves Legions were nearing Terra; and the Ultramarines were only a short distance behind.At that moment, Horus despaired; his gamble had failed, solar weeks of further conflict would be needed to break the defenders and the Emperor's reinforcements would arrive in mere hours.What happened next is disputed in the Imperial historiography of the Horus Heresy; some believe Horus disabled his void shields as he experienced one last moment of regret for his betrayal of his father and his turn to Chaos, while others believe it was a personal challenge to the Emperor.Nevertheless, Horus lowered the void shields of his great vessel, the Gloriana-class Battleship Vengeful Spirit. The lowering of these shields was detected by the Loyalist vessels in orbit and the information was relayed to the Imperial Palace.The Emperor of Mankind rose to the challenge, leading his elite personal guard, the Adeptus Custodes, the Primarchs Sanguinius and Rogal Dorn, and several companies of Imperial Fists and Blood Angels Veteran Space Marines in the assault and teleported aboard the Vengeful Spirit.Horus used his Warp-fuelled powers to scatter the Emperor's force throughout the massive warship when they teleported up through the Warp. Each fought a series of battles against the forces of Chaos aboard the corrupted starship, attempting to link up with their comrades and confront Horus.It was Sanguinius who reached his brother Horus first. The Warmaster attempted to turn the Blood Angels' Primarch, his oldest and closest friend among the other Primarchs, to Chaos one last time.When Sanguinius refused to be corrupted, Horus attacked. Wounded from his many battles on Terra and the terrible battle with the daemon Ka'bandah, Sanguinius proved to be no match for Horus, now at the peak of his daemonic power after his long alliance with the Ruinous Powers.Horus strangled the Angel of Baal with ease. An alternate version of this event sometimes recorded in the Imperial records has Sanguinius cutting a small hole in the Warmaster's Power Armour before he died, and this hole provided crucial aid in the Emperor's final defeat of Horus.When the Emperor of Mankind finally entered the throne room of the Vengeful Spirit, He saw the winged corpse of the angelic Sanguinius lying at Horus' feet.Horus called the Emperor foolish for refusing the power that the Chaos Gods offered to men, and timid for not taming them to his will if He was truly the Master of Mankind as he claimed. Horus proclaimed that if the Emperor would kneel before him, then he would spare His life.But the Emperor, tens of millennia older than His misguided and once beloved son, knew well the trap that had snared Horus. The Emperor told the corrupted Primarch that he was the deluded slave of Chaos, not its master, for no mortal could ever truly claim to be more than simply a pawn of the Ruinous Powers.Snarling, Horus hurled bolts of daemonic lightning at the Emperor, but the Emperor nullified them with his own immense psychic abilities. The die was cast. Each god-like being knew that the fate of humanity now hung in the balance.The Emperor and Horus engaged one another in the throne room of the massive battle barge, a battle that was both physical and psychic in nature. Though the Emperor's psychic gifts and martial skills were unequalled, He found himself unwilling to summon his full strength against His beloved son.The Emperor suffered grievous wounds at Horus' hands, and after a score of thrusts, parries and counter-thrusts between the Emperor's Runesword and his own Lightning Claw, Horus sliced open the Emperor's chest armour, then sliced his jugular and severed the tendons in his right wrist, disarming the Emperor.A psychic blast seared the flesh from the Emperor's face, destroying one of the Master of Mankind's eyes. After tearing the Emperor's right arm from its socket, Horus raised his father high over his head, and broke His back over his knee.At that moment, a lone Loyalist warrior entered the bridge, just as the Emperor fell. Horus, gloating in victory, showed the Imperial warrior the Emperor's broken form and laughed, taunting the Loyalist's uselessness and defeat. The valiant Imperial warrior, far from being daunted, roared in defiance and interposed himself between the Emperor and the Warmaster, heroically holding the line against the Chaos-corrupted Primarch. He was flayed alive for his defiance by a glancing psychic blast from Horus.The exact identity of the brave warrior is a source of much debate amongst Imperial historians, for today only the Emperor knows the truth. The Adeptus Ministorum tell the story that it was a lone Imperial Army trooper named Ollanius Pius who held the line, going as far as to canonise the man as the Guardian Saint of the Astra Militarum in the 32nd Millennium, yet many doubt that mere humans would have accompanied the Emperor and His Primarchs to confront Horus.The Imperial Fists maintain it was one of their Terminators who challenged Horus, however some see this as a desperate attempt to lessen their collective guilt stemming from the fact that Rogal Dorn never could participate in the fighting. Most savants now agree that it was probably one of the Legio Custodes who interceded, yet the other stories continue to be told and retold over the whole of the Imperium of Man.The casual brutality of the Warmaster's act galvanised the Emperor as He realised what awaited Mankind under the rule of Horus and the Chaos Gods. Realising at last that His favoured son was truly lost to the corruption of Chaos, the Emperor finally gathered His full and awesome psychic power in the Immaterium and unleashed a lance of pure Warp energy that pierced the gloating Horus' psychic defenses and ripped his body apart.In some versions of the tale, this blast was only able to pierce the Warmaster's body through the hole that had been made by Sanguinius before his death. Just before Horus died, he looked his father in the eye, shedding a single tear, begging his father to forgive him for his betrayal.The Emperor saw regret in His fallen son's eyes. The Emperor also knew that the Ruinous Powers could attempt to possess Horus again, and that He would not be there to stop him if they did. Driving all of the near-infinite reserves of compassion from His mind for the sake of the humanity He had served and loved all the years of His long life, the Emperor summoned his power once more and destroyed Horus utterly, his essence burned from existence so that the Ruinous Powers could not resurrect him as a Daemon Prince through their claim on his soul.The destruction of Horus' soul sent a psychic shockwave surging across the Sol System, casting the daemons of Chaos back into the Warp, and spreading mass panic among the Traitor Legions and other Traitor forces on the surface of Terra in seconds as the Chaos Gods found their powers disrupted temporarily by the death of their favoured mortal vessel.It became clear to the forces of Chaos that their champion had been defeated. A terrible, berserk fury later known as the "Black Rage" had encompassed the Blood Angels at the moment of their Primarch's death, and they were surging forth to scatter the attackers.Retreat turned to rout, and rout soon turned to bloodbath; thousands upon thousands of Traitor Space Marines and Titans fell attempting to flee. The ground before the Sanctum Imperialis ran red with the blood of Traitors and Heretics.The Traitor forces made their way back to their dropships and prepared to flee the Throneworld. It is said that the Primarch Angron took one final, longing look at the Imperial Palace the Traitors had almost seized before he boarded his own drop ship. Reports from the time indicate that the Sons of Horus, sensing the moment of their Primarch's death, immediately broke from the siege and were the first to flee from Terra, while Mortarion and the Death Guard Legion were the last.Meanwhile, on the Vengeful Spirit, the Primarch Rogal Dorn finally found his way to the corrupted starship's bridge, only to discover his fallen brother, Sanguinius, and the shattered body of the Emperor, who was now on the verge of death, His remaining psychic energy spent in the battle with Horus.It was then that the Emperor whispered instructions to Dorn, urging the Imperial Fists' Primarch to take Him to the device known as the Golden Throne in the inner sanctum of the Imperial Palace.The surviving Loyalists teleported back to the Imperial dungeons beneath the Imperial Palace. Here Malcador the Sigillite, the Regent of Terra who was himself the second most powerful human psyker, had briefly taken the Emperor's place on the Golden Throne, thus keeping the Warpgate to the extension of the Webway that the Emperor had been building on Terra for the benefit of humanity safely closed.As Malcador's body was being removed and the Emperor was put into his place, the Regent of Terra's body began to collapse to dust from the sheer strain of holding back the dangers of the Immaterium from coming through the Webway gate and assaulting Terra.Yet, the Sigillite somehow managed to impart his final remaining psychic energy to the Emperor before his death to restore the Master of Mankind's to consciousness for a final time. Suddenly awakened, the Emperor delivered His final instructions to His servants before being interred in the device as the Adepts of the Mechanicum furiously worked to modify it to the Emperor's specifications.The Emperor spoke his final words to his followers. He urged them to continue the fight to free humanity from Chaos and the machinations of the Ruinous Powers as well as the ignorance that continued to assail it. And then the Master of Mankind spoke no more, His body entombed within the life-support mechanisms of the Golden Throne, His spirit caught between the Warp and a crippled, decaying body for millennia.Unable to complete the Webway project that the Golden Throne had originally been intended to create and maintain, the Emperor now chose to use its psychic augmentation mechanisms both to maintain his shattered body's life support functions and to project his mind into the Immaterium where He would create and maintain the Astronomican navigation beacon to hold the Imperium together and battle the Chaos Gods on their own plane, always seeking to protect Mankind from their corruption and depredations.The Imperium of Man had survived the Horus Heresy intact, but would evolve into the bastion of repression and brutality the Emperor had long fought against without His direct, guiding hand upon it.In this, at least, the Chaos Gods had won a partial victory, for this state of affairs would ensure that their temptations would continue to corrupt the weaker members of the human race and prevent the final establishment of a new and better order across the galaxy.Yet, for all its terrible and growing flaws over the next ten millennia, the Imperium would also offer humanity its best and perhaps only hope for survival in an uncaring and increasingly hostile universe.