The Siege of Terra phase by phase

On the first day of 014.M31 Horus’s Great Armada entered the Sol system, opening the Solar War against Dorn’s five concentric Spheres of defence. The Sons of Horus under Horus Aximand fell upon Pluto — Sigismund was wounded but, teleporting away, severed Aximand’s arm. At the same time the siege of the ancestral Inwit cluster tied down the Imperial Fists’ reserves far from Terra.

Perturabo’s Iron Warriors stormed Uranus while Jubal Khan’s White Scars held the void above the galactic disc. Dorn traded space for time, but Abaddon, ramming with the “War Oath”, broke through Luna’s defensive ring and scattered the Solar fleet. With the fall of Luna, Terra lay exposed to orbital bombardment; in the captured system the crew of the “Sisypheum”, at the cost of almost all their number, rescued the gene-artefact “Magna Mater” from Luna.

To seal the breach in the webway beneath the Palace, around a thousand psykers were sacrificed on the Golden Throne. The breach was closed, but the price was that the Emperor became bound to the Throne for ever and could no longer take the field.

Perturabo opened a bombardment of the orbit lasting many days, probing for a flaw in the Palace’s void shield, the Aegis. This cannonade opened the ground siege of the Imperial Palace and became the prologue to the first assaults on the walls.

Nine “Ark Mechanicus” ships landed the Death Guard by the Palace, and the trenches were engulfed by pestilence and poison gas. The Aegis shield fell, daemons descended upon Terra, and Angron came crashing down from the heavens for the first time — the siege entered a new, putrescent phase.

The first section of the Imperial Palace — Helios Gate — was seized by the traitors. The breakthrough forced the defenders to pull their defence inwards, to the next lines.

The most heavily fortified spaceport on Terra fell to the traitors’ onslaught, and Mortarion made it his headquarters. The capture gave Horus his main bridgehead for landing reserves right at the walls of the Palace.

At Gorgon Bar Sanguinius smashed a Titan of Legio Vulpa with the Spear of Telesto and beat off the first assault, yet the fortification fell all the same. A strike by the Iron Warriors levelled the Magnifican, depriving the loyalists of cover, and perpetual night descended on Terra.

Dorn’s carefully laid trap at the Saturnine Gate cut down the Mournival: Aximand, Kibre and Tormageddon were killed. The decisive loyalist victory bought weeks of defence and split Horus’s inner circle.

While the assault on the Saturnine Gate was failing, another line fell — Colossi Gate, followed by the Eternity Wall Spaceport, where Angron was torn to shreds by gunfire and at once reborn. Against the backdrop of these losses, ten thousand Dark Angels under Corswain fought their way through to Terra — a rare reinforcement for the besieged loyalists.

Disgusted by the war of daemons, Perturabo led the Iron Warriors away from Terra, and the Death Guard took their place. Meanwhile Corswain’s Dark Angels fought Typhus at the Hollow Mountain to relight the Astronomican and let the loyalist reinforcements find their way to Terra.

Legio Mortis destroyed Legio Ignatum and broke through the Exultant Wall, opening the road to the Sanctum Imperialis. At the same hour on Titan, a moon of Saturn, Malcador raised eight Grand Masters and founded the Grey Knights — mankind’s secret weapon against Chaos.

Jaghatai Khan beheaded Mortarion and banished him into the warp, retaking the Lion’s Gate Spaceport for the landing of Guilliman’s reinforcements. Vulkan overcame Magnus in the webway, while at the Eternity Gate Sanguinius broke Ka’Bandha’s spine and banished Angron — the line held, but the Angel was deathly weary.

Horus lowered the shields of the “Vengeful Spirit”, luring the loyalists aboard: Sanguinius reached him first and was killed, refusing to betray the Emperor (this is how the Black Rage was born). Then the Emperor destroyed Horus at the cost of mortal wounds, and Dorn carried Him to the Golden Throne — while Erebus, with a final betrayal, stabbed Loken, (re)creating the daemon Samus.

The Ultramarines fleet swept aside the retreating traitor armada, and Guilliman convened a Council to rebuild the Imperium. The Ultramarines retook Luna — the first battle of the Great Scouring; thus began a seven-year purge that drove the traitors into the Eye of Terror and opened the Long War.