Siege of Terra (Detailed) 4

Despite this setback, Horus remained undeterred. He organised a massive attack by the Legio Mortis, Sons of Horus, Chaos Knights, and Dark Mechanicum war engines against the Mercury-Exultant Kill-zone, a 150 km-deep No Man's Land before the Exultant Wall which connects the Inner and Outer Palaces. This massive force was met by some 50 engines of the Legio Ignatum[15a], including the Emperor Titans Imperious Prima, Exemplis, and Magnificum Incendius. This formidable army was aided by not only the shattered remains of other Titan Legions such as the Legio Solaria, Legio Atarus, Legio Defensor, Legio Amaranth, Legio Gryphonicus, and Legio Invigilata but also dozens of Knight Houses and supporting Imperial Army and Secutarii.[15b] The Ordo Sinister also finally agreed to enter the fighting, sending a Warlord-Sinister Psi-Titan to the Ignatum's aid.[15d] In the ensuing apocalyptic battle, the Traitors first attacked with waves of destroyed Titans that had been resurrected through sorcery. These "zombie" Titans now walked without a living Princeps, and were largely used as cannon fodder by the Traitors due to their ability to absorb enormous amounts of punishment.[15c] In their wake came the Legio Mortis and endless swarms of Dark Mechanicum vehicles and Daemon Engines. They were led by the Dies Irae and its bodyguard of 7 Warlord Titans.[15b] Despite the devastation wrought upon by the Traitors, thanks to orbital bombardment, new Warmaster Titans, weight of numbers, and madness spread amongst the loyalist mortal crews, the Traitors ultimately prevailed in annihilating the Legio Ignatum and its allies and reaching the Exultant Wall.[15e]

Jaghatai Khan confronts Mortarion at the Lion's Gate Spaceport[20g]

Horus ordered his army to push on and had the attack on the outer walls of the Imperial Palace be spearheaded by the Death's Head Titan Legion. Losing five Titans within minutes to entrenched loyalist defenses, the traitor forces would not relent and kept hammering away at the palace walls. A counterattack against the Chaos horde's flanks by loyalist titans failed, though the White Scars took advantage of the confusion it caused to sweep down at the traitor forces rear columns and wreak havoc.[2] The Siege of the Imperial Palace soon ground on for many days, with the two primary attacks during this time being made by Angron and his World Eaters supported by Daemon Engines in one sector and the Legio Mortis in the other.[1c]

Under a vicious combined attack by the World Eaters and Legio Mortis, major breaching attempts were made at the Mercury and Exultant Wall zones. The traitors laid plasma bombs, which when detonated caused a chain reaction that cooked off the ammunition of the wall defenders. The resulting blast was so massive that it easily dwarfed atomic weapons and caused both warring armies to briefly go silent in shock and awe. A 300 meter long section of the wall collapsed, causing a landslide that buried loyalist and traitors alike. Kharn's 8th Assault Company was the first to climb the rubble and move through the gap as Knights and Legio Mortis Titans swarmed behind. The World Eater Skarr-Hei was the first through.[15k] The way to the Sanctum Imperialis was now clear and the loyalist defenders seemed doomed, with many seeing the battle now as a suicidal final stand rather than one in which they could emerge victorious.[20a]

Battle for the Astronomican

Meanwhile, the force of Dark Angels under Corswain remained in the fringes of the Sol System, rendezvousing with Admiral Niora Su-Kassen and her hidden fleet led by the Phalanx. It was agreed that the Dark Angels should make for Terra to aid the defenders, but they would need something significant in order to break the traitor blockade of the world. Su-Kassen provided the enormous Battle-Carrier Imperator Somnium, the former flagship of the Emperor himself. The ship was largely evacuated of crew and sent plummeting towards the traitor fleet as the Dark Angels vessels hid in its wake. Though torn apart by enemy fire, the mighty Imperator Somnium was able to destroy four World Eaters Heavy Cruisers and an Emperor's Children Battle Barge. Afterwards, the explosion of the Emperor's ship heavily damaged the Terminus Est and the Conqueror battleships.[15f]

The Dark Angels vessels were able to launch a Drop Pod landing operation to deliver their warriors to Terra, with Corswain's force landing upon the Hollow Mountain. Battling through the Emperor's Children and many warp-spawned horrors inside the Fortress including the Daemon Vassukella, Corswain was able to establish contact with Dorn and announced his intent to attempt and reactivate the Astronomican.[15g] Subsequently, Corswain and his Dark Angels found themselves besieged by traitor forces and struggling to hold the Astronomican.[22b]

Retaking the Lion's Gate Spaceport

The grim outlook of the chance for victory was not shared by the White Scars and their Primarch, Jaghatai Khan, who continued to talk of life after they had won the battle.[20a] Not content to simply hide behind walls, the Khan at last decided at this desperate final hour to make his move. He became committed to retaking the Lion's Gate Spaceport, which if captured would allow Guilliman's coming reinforcements to quickly land on Terra as well as slow the flow of traitor forces. Overworked and exhausted and knowing he could not control his brother, Rogal Dorn did not try to stop the Khan. Facing the White Scars were the bulk of the Death Guard under Mortarion, who had taken up Lion's Gate Spaceort as his new headquarters since the departure of Perturabo.[20b]

For the operation to recapture Lion's Gate, the Khan mustered not only nearly the entire White Scars Legion but also the Terran First Armoured and the Sky Fortress, the last Orbital Plate on Terra that until now was being used as an airborne carrier and fire support platform. After much careful planning, the Khan struck with an overwhelming push by thousands of Imperial Army tanks protected by White Scars infantry. In their wake came a massive charge of White Scars Jetbikes. Gold Battlefront under Ganzorig Noyan-Khan struck an arrowhead across the northern sections of the space port approaches, while Ebony under Qin Fai Noyan-Khan attacked the southern flank. Jaghatai Khan himself led Amber Battlefront through the center and directly into the thickest enemy defenses.[20c] The ensuing fighting was ferocious, even for the standards of the Siege. The Sky Fortress was able to fulfil its mission to provide fire and aerial support for the White Scars until it was shot down, crashing into the Imperial Fleet College and creating a massive explosion. While the White Scars and Imperial Army tanks were able to quickly push to the Lion's Gate Spaceport, inside their advance began to become bogged down by the stubborn defenses of not only the Death Guard, but also their Daemonic and Mutant allies. A war of attrition broke out, one in which the White Scars were ill-suited but the Death Guard excelled at.[20d]

As loyalist casualties mounted, the Khan was able to fight his way into the heart of the Spaceport and confront Mortarion himself. The old enemies exchanged few words before engaging in a final duel. Faced with Mortarion's new Daemonic endurance and strength, the Khan was brutally beaten down and nearly defenseless. However he was able to find a weakness in the Death Lord with his pride. Jaghatai Khan scolded Mortarion for being weak and giving into the powers of the Warp, while he himself had resisted the temptations of Chaos and remained true to the Emperor. Mortarion flew into a rage, which the Khan took advantage of to launch a second wave of dizzying attacks that overwhelmed the Primarch. In the end the badly wounded Jaghatai Khan was impaled on the blade of Mortarion's scythe, but simply pulled his body along its length to get face-to-face with the Death Guard Primarch. The loyalist Primarch decapitated Mortarion, who was banished into the Warp in a massive explosion similar to that of a Vortex Weapon. Later, the Khan's badly wounded body was discovered by Ilya Ravallion and Jangsai Khan.[20e]

In the aftermath of the Khan's seeming death, the White Scars were thrown into a frenzy and prepared to throw their lives away in a final charge against the Death Guard. The sudden tenacity surprised the Death Guard, who without Mortarion to guide them were forced back. Thanks to the efforts of Ilya Ravallion and Shiban Khan the White Scars decided to remain at Lion's Gate Spaceport and secure it for the loyalists instead of pressing on into certain death.[20e] Meanwhile, the surviving Death Guard rallied under Typhus, who had stationed himself just outside the battlezone.[20f]

Last Stand at the Eternity Gate

Despite the retaking of the Lion's Gate Spaceport, the situation continued to degrade for the loyalists and nothing could stop the tide of traitors pouring into the Inner Palace from the parts of the Ultimate Wall broken open by the Legio Mortis. Even the Bhab Bastion, Dorn's command center, became besieged with the Imperial Fists Primarch still inside. By this point the traitor armies have lost much of their cohesion, turning into a barbaric horde that swept forward murdering all in its path. The Emperor's psychic shield was near-breaking point thanks to a constant immaterial assault by the debased form of Magnus in the Webway. To try and stop the Crimson King, Vulkan was dispatched into the Webway to find and kill Magnus before he could succeed. As whoever could fled towards the Sanctum Imperialis Horus himself appeared over the traitor communications network for the first time in weeks to give a single order to his forces: the capture of the Eternity Gate at dawn.[22b][22c]