As a vast traitor horde of traitor Astartes, Imperial Army, Beastmen, Mutants, Daemons, Titans, and other horrors massed on the horizon, only some 70,000 defenders mustered on the Delphic Battlement before the processional to the Eternity Gate. These were mainly Blood Angels and Imperial Army, but Imperial Fists, White Scars, Legio Ignatum, and Mechanicum loyalists were also represented. Corswain offered to send his own forces defending the Astronomican to aid the defenders, but Sanguinius declined their offer, due to the vital nature of the Dark Angels Paladin's mission.[22a]
Faced with certain death before the vast traitor horde, Sanguinius nonetheless organised a defense to try and buy precious time. At dawn the traitors erected the mutilated but still-living loyalist prisoners they had nailed to banners, crosses, vehicles, or whatever else they could find to try and break the spirit of the defenders. Next marched forth the Daughter of Torment, a Reaver Titan of the traitorous Legio Mordaxis. In its Power Claw was the tortured form of Blood Angels Captain Idamas. It issued forth Horus' conditions, that any who fled the coming battle would be granted a pardon by Horus, new Emperor of mankind. Sanguinius responded with a rousing speech to the defenders, stating that he would stand and fight but all others were free to go where they wished. Inspired or perhaps shamed by the Great Angel, it is believed that no loyalists took the opportunity to leave and instead all present pledged themselves to Sanguinius. The Blood Angels Primarch next took to the skies and beheaded the Daughter of Torment as battle erupted.[22d]
The battle that followed was immense. The traitor horde surged forward as the guns of the Delphic Battlements opened up. The initial waves were decimated, but through weight of numbers they began to reach the walls. A Khornate Warlord Titan docked with the Delphic wall, vomiting forward World Eaters from its mutated mouth. Chaos erupted in short order as the battle turned into a savage melee. Into this strode the Bloodthirster Ka'Bandha, who had been bested by Sanguinius during the Signus Campaign. Vowing to reap 500 Blood Angels in the presence of their Primarch, the Daemon nearly succeeded before Sanguinius intervened. The two had a dramatic airborne battle that ended when Sanguinius broke the Daemons back with the hilt of his sword. Ka'Bandha plummeted to the earth, consumed by lesser Daemons taking advantage of his weakness.[22e]
With the traitor horde still advancing and Daemons now manifesting even inside the Sanctum Imperialis itself Custodian Tribune Diocletian Coros ordered the Eternity Gate shut. However it was then that Legio Audax Titans intervened, using their Ursus Claws to force one of the doors open. Sanguinius was about to cut these chains when Angron surged from the sky, directed by Horus himself to kill his brother. Already weakened by his fight with Ka'Bandha, Sanguinius fought a desperate battle against Angron but managed to initially hold his own. After a climatic airborne battle, Angron impaled Sanguinius upon his Black Blade. However Sanguinius used the opportunity to rip out Angron's Butchers Nails, causing the Daemon Primarch's head to explode. With Angron banished into the Warp, the World Eaters lost whatever sanity they had and began to cut down their own allies. This combined with the defeat of Magnus in the Webway at the hands of Vulkan broke the traitor advance just short of the Eternity Gate, which managed to finally seal shut as the surviving loyalists fled inside.[22e][22f]
Just moments after the battle of the Eternity Gate, Shiban Khan and his White Scars managed to reactivate the anti-orbital defenses of the Lion's Gate Spaceport. The traitor armada, hanging in low-orbit, was subjected to a vicious ground-to-orbit bombardment. Word reached the Sol System that Roboute Guilliman was just one week away, with Leman Russ, Corax, and Lion El'Jonson not far behind.[22f]
Despite the victory at the Eternity Gate, the situation for the loyalists was still dire and Chaos forces were advancing all fronts. Remaining loyalist officers such as Fafnir Rann, Zephon, Nassir Amit, Maximus Thane, and Namahi led desperate but futile defenses of the last battlements inside the Inner Palace. While nearly all order and discipline had by now broken down amongst the Traitor Astartes, vast Daemonic legions spilled forth as legendary figures such as Be'lakor, Skarbrand, Ulkair, N'Kari, Heartslayer, Drach'nyen, Epidemius, Ku'gath, Madail, Karanak, The Masque, Doombreed, Tallomin, and Skulltaker manifested on Terra's soil.[24a] Just hours after the shutting of the Eternity Gate, the Bhab Bastion itself was overrun by Sons of Horus forces under Tarchese Malabreux and Rogal Dorn was forced to retreat into the Sanctum Imperialis.[24b] Concepts such as time and space started to break down and mere hours passed as if it were weeks as Terra itself began to slowly be sucked into the Warp, with the Vengeful Spirit as its conduit.[24c] All across Terra, traitor armies and maddened souls began to chant the name of the "Dark King". This new being would become the fifth God of Chaos born from Humanity just as Slaanesh was born from the Eldar.[24d]
The Emperor must die ~ Traitor chant in the final stages of the Siege[24d]
The Vengeful Spirit
It was at this moment that Horus finally emerged from Lupercal's Court for the first time since the Siege began, apparently in a half-lucid stupor and imagining himself back on the Great Crusade. Journeying to the bridge of the Vengeful Spirit, he addressed his equerry Kenor Argonis as Maloghurst, saw long-dead Zardu Layak at his side, and stated he would finally finish the war. To the shock of all present, Horus stated that he had apparently lowered the Vengeful Spirit's Void Shields, inviting the Emperor himself to Teleport aboard his flagship. This would allow Horus to slay the Emperor before reinforcements under Guilliman could arrive, which were mere hours away. With their Emperor dead, Guilliman's incoming fleet would lose heart and scatter before the forces of the Warmaster.[24e] However, Guilliman's fleet was still having difficulty finding Terra without the Astronomican, which Corswain and his Dark Angels sought to reactivate. To thwart the Dark Angels, Typhus led a massive Death Guard assault upon the Hollow Mountain.[24j]
Upon discovering the shields of the Vengeful Spirit down, Malcador the Sigillite alerted the Emperor, still struggling to keep the Golden Throne and its adjoining Webway Gate stable. Upon learning of the news, the Emperor knew it was time to act and end Horus, even though he was certain it was a trap. Rogal Dorn, Sanguinius, Vulkan, and Valdor were all called to his side for the coming battle, and all objected to the Emperor's plan to personally teleport aboard the Vengeful Spirit.[24f] However the Emperor overruled his sons, commanding Valdor and Dorn to come with him while Sanguinius took control of loyalist forces on Terra and Vulkan stay behind to oversee the potential failsafe on the Golden Throne.[24g] Sanguinius flatly objected to his fathers request to stay behind, telling the Emperor of his prophetic death at Horus' hands and his intention to defy fate by defeating his traitorous brother instead. This was enough to move the Emperor to change his mind. Four company's were organised for the assault: the Hetaeron Guard led by the Emperor, another Custodes company under Valdor, a mixed force of Sanguinary Guard and Blood Angels 1st Company under Sanguinius and Raldoron, and Huscarls under Dorn and Diamantis. The operation was codenamed Anabasis.[24h] Malcador took his place upon the Golden Throne in the Emperor's place, an act that would cost him his life. For that, The Emperor renamed Malcador the Sigillite to Malcador the Hero.[24i]
While the Emperor led the assault on the Vengeful Spirit, Archamus was placed in command of the reamining loyalist forces on Terra. Meanwhile at the Astronomican, Corswain and The Lord Cypher waged a battle against a Death Guard assault led by Typhus, who was attempting to stop the reactivation of the Astronomican. If the traitors succeeded, Guilliman's armada would have no way of reaching Terra in time.[24j] For the traitors part, upon discovering their flagships shields were down, Abaddon abandoned the war on the surface along with the last few remaining sane Sons of Horus officers to rush to his fathers side.[24p]