Black Legion - The Horus Heresy: The terrible galactic civil war that followed and lasted for nine Terran years of genocidal death and destruction on a scale never before witnessed by Mankind, called the Horus Heresy by later generations, was the most terrible conflict in the history of the Imperium, and came close to shattering it forever. This conflict quickly became a terrible war of escalation and retaliation. The Legions struck desperate blows against each other across the length and breadth of the nascent Imperium.By the time Horus had carved a bloody path to Terra, the Sons of Horus stood at the head of a vast army of Traitor Space Marines. In a battle the likes which the Imperium has never seen since, Horus' armies fell upon the Emperor's Imperial Palace and Abaddon was granted the honour of leading them into battle. This was to be the zenith of the Sons of Horus' power. Never again would the Legion gather in such strength or grandeur on the field of battle.In the cauldron of war, Abaddon led the 1st Company and the hulking, black-armoured Terminators of the Justaerin into the Emperor's Palace, smashing through the loyalist defenders. Their Chainfists and Power Swords dripped with gore, any who dared stand against them were torn apart. Everywhere, the fires of the Heresy burned out of control; Titans traded blows over the ruined walls of the palace and great warships filled the sky with dazzling lance fire, raining bombardments upon friend and foe alike.Horus watched the battle unfolding below from the shrouded bridge of his flagship, the Vengeful Spirit. On flickering holo-charts, the Warmaster saw his armies trapped against the inner walls of the Emperor's palace, Loyalist reinforcements arriving with every passing solar hour. Through the vista panes of his bridge, he could see that the battle in Terra's orbit was also turning against his fleet. Horus knew time was running out.In his arrogance and anger, the Warmaster made one last gambit, lowering his ship's Void Shields so that Emperor could teleport aboard and face him personally. He was not to be disappointed. In an incandescent blast of light, the Emperor teleported onto the Vengeful Spirit seeking out His traitorous son. The battle between the two great warriors exchanging titanic ringing blows even as their psychic selves struggled in the Warp. For all his rage and anger, Horus could not win -- though before the Emperor obliterated His son's soul, Horus delivered a mortal blow to his gene-father.Abaddon was climbing over the heaped corpses of broken Imperial soldiers when he felt the psychic howl heralding the death of his Primarch. Every Son of Horus knew at once that their Warmaster had fallen, thousands of warriors pausing in battle to look up into the burning sky. The news spread like a contagion through the Traitor Legions, and the assault that had come so close to success began to collapse.Abaddon immediately teleported back onto the flagship and arrived at his master's side in time to rescue Horus' body. With a cry of deepest pain and anguish, Abaddon vowed vengeance against his father's killer. Tearing free the Lightning Claw from Horus' arm, he fixed it to his own, symbolically taking up his Primarch's debt of blood against the Emperor.Realising the battle for Terra was lost, Abaddon moved to save the XVIth Legion from annihilation. He fought his way through the remaining loyalists aboard the Vengeful Spirit and cleared the ancient vessel of resistance, the mortally wounded Emperor already borne back to Terra by the Imperial Fists' Primarch Rogal Dorn. Laying claim to the Vengeful Spirit, Abaddon and the Sons of Horus broke orbit and fought their way free of the battle and escaped into the void.