Harrowing of Pyrrhan
| 2/3rd of the total strength of the Blood Angels
| System-sized Fortress|
Near-endless Daemonic hordes
The Harrowing of Pyrrhan was a battle during the Horus Heresy.
Following the dissolution of Imperium Secundus the three Primarch's within Ultramar, Roboute Guilliman, Sanguinius, and Lion El'Jonson, attempted to journey to Terra and aid the Emperor against Horus. However to do so they would have to move their fleets through the Ruinstorm, a feat considered near-impossible. Nonetheless 2/3rds of the Ultramarines, Blood Angels, and Dark Angels departed Ultramar and set course for Terra. After many weeks of ineffectual Warp jumps that even Lion El'Jonson's Tuchulcha had difficulty navigating, The Ultramarines came into possession of several Chaos-corrupted Navigators after the Battle of Anuari. Unlike their loyalist counterparts, traitor Navigators had far less difficulty navigating the Warp and were surprisingly quite eager to lead the loyalist fleet through the Ruinstorm.
While in the Warp, the three loyalist fleets were forced to drop into the Materium due to the presence of a massive "barrier". Once within realspace the barrier shocked even the Primarchs. A massive floating fortress of pure Chaos the size of a solar system stood in the way of the loyalists. Its walls were millions of miles thick and billions of miles long and adorned with war horns and sigils the size of gas giants. Faced with such an impossible construct, even the combined orbital bombardment of all three loyalist fleets were completely ineffective and with the Ruinstorm raging around them, no alternate route around the construct could be found. The only option was to somehow breach a part of the fortress. Sanguinius, realizing that no such construct could possibly have been made by Human or even xenos hands, deduced that it was of Warp origin and anchored to the Materium through the daemonic forges of the world of Pyrrhan, which was located below a massive "gate" along the fortress' walls. Sanguinius convinced Guilliman and Lion El'Jonson to launch an assault on Pyrrhan and hopefully banish the maddening edifice back to the Warp.
The loyalists made a mad dash towards Pyrrhan, with many ships claimed by the planetoid-sized gun emplacements of the Daemonic Fortress. Once within close orbit of Pyrrhan the loyalist fleet was able to maneuver itself into a blindspot, and avoided the fortress' fire. However despite the combined armies of three Legion's, Pyrrhan was defended by seemingly endless hordes of Daemons spread out across daemonic forges the size of continents. Destroyer Squads from the Ultrmarines led the vanguard of the attack, followed by disciplined firing lines of the Dark Angels. Lastly the Blood Angels launched a Drop Pod and gunship assault into the central Manufactorum complex, hoping to find some way to shatter the Daemonic anchors.
Under heavy air support and led personally by Sanguinius, the Blood Angels managed to advance to the central gate of the largest manufactorum complex as the Ultramarines and Dark Angels battled on their flanks. The Blood Angels managed to enter the complex just before the doors sealed shut behind them. The Lion led his legionaries to the regions before the closed doors of the forge. The formations of Dark Angels were walls of black iron. The daemons hurled themselves against the barriers. The Dark Angels refused to give up a single step of the land they held. Their heavy artillery bombarded the swarms of monsters, and the infantry advanced methodically towards the enemy. Towards the middle of the battlefield and at the southern end, the greater body of the Ultramarines attacked in two radiating movements. Phalanxes cut into the enemy. Guilliman forced the daemons to contend with multiple fronts and kept them on the defensive. They sought to repel the invaders and take back the land. The Ultramarines had no positions to hold. All they needed to do was keep moving, and destroy everything in their paths.
Meanwhile inside the manufactorum, Sanguinius and the Blood Angels found a factory of madness and endless amounts of Daemons that seemed to materialize out of thin air. Nonetheless they made a slow but painful advance, but despite Melta Charge detonations they couldn't find a way to destroy the facility. Sanguinius soon found himself isolated and in battle against a Herald of Tzeentch. During the struggle, the Angel was overcome with prophetic visions of his eventual death by the hands of Horus. Sanguinius relived his death a thousand times in the blink of an eye, but in a single alternate fate managed to strike down Horus with his Blade Encarmine. Within reality, Sanguinius swept his blade down and killed not only the Herald of Tzeentch, but the heart of the Manufactorum facility. The compound began to collapse, and the Blood Angels narrowly escaped before it imploded. When the Manufactorum died, Pyrrhan itself began to collapse. The three Space Marine Legions managed to evacuate back into their ship as Pyrrhan exploded.
With Pyrrhan destroyed, the massive gate at the center of the Daemonic Fortress collapsed. This allowed the loyalist fleets to rush through the gap, outrunning the gargantuan gun emplacements of the bastion. The loyalist fleets eventually managed to reach the center of the Ruinstorm at Davin.