Fallen Angels - Betrayal: In the aftermath of the Horus Heresy, the surviving Loyalists rallied the reeling Imperium. The Dark Angels took a significant part in these battles, which later came to be called the Scouring. As they pursued the rebels, the Legion diverted to nearby Caliban, which had been enshrouded by Warp storms since Horus' betrayal.For Lion El'Jonson, one final act of treachery remained to be discovered. The Dark Angels arrived too late to take part in the epic Siege of Terra, where Horus was defeated and the Emperor grievously wounded, his shattered body placed within the life-support mechanisms of the arcane device known as the Golden Throne. Grief-stricken, Jonson returned to Caliban.As the Dark Angels fleet moved into orbit, they were met by a devastating barrage of planetary defence laser fire. Stunned by the ferocious attack, Jonson withdrew his vessels from orbit and attempted to find out what had happened on his homeworld.A nearby merchant starship soon provided the answer: Luther had apparently ordered the approaching fleet fired upon. His reasoning for this action was unknown to the primarch, though it was suspected that Luther, like many of the Lion's brothers in the defeated Traitor Legions, had been corrupted by Chaos. The fury of the Lion and his Dark Angels at what they perceived as a terrible betrayal knew no bounds; Jonson himself immediately ordered a sustained orbital bombardment of the Traitors' positions and led an attack against Luther's bulwark at the Dark Angels' fortress-monastery personally.In the resulting battle, the two adversaries struck blow upon blow against each other, tearing down the Dark Angels' fortress-monastery around them until nearly the whole massive edifice had been levelled by their battle. Meanwhile, the massed guns of the Dark Angels' fleet pounded the planet, until the very surface of Caliban began to crack under the strain of the orbital bombardment.As the planet itself started to break apart, the battle between the Lion and Luther reached its climax. Luther, apparently aided by the Ruinous Powers of Chaos, unleashed a furious psychic attack that knocked Jonson to his knees and left him mortally wounded. But as the dying primarch struggled to stand, his noble features wracked with pain, it was as if a curtain had been lifted from Luther's eyes and he realised the full extent of what he had done and the duplicity of the Chaos Gods.Devastated, the realisation shattered Luther's sanity and he slumped down beside Jonson, no longer willing to fight. Soon after Luther's breakdown, a Warp Storm of unprecedented fury engulfed Caliban as the Ruinous Powers sought their revenge for Luther's failure to slay the Lion. In an uncontrollable flood of psychic energy, the Warp rushed into the physical universe.The immense strain these forces placed upon the planet, in combination with the tectonic shifting and cracking caused by the Dark Angels' orbital bombardment, caused the horrific destruction of the entire planet; Caliban itself shattered, breaking into countless chunks of dead and dying rock.The Fallen Dark Angels who had served under Luther were sucked from the face of Caliban into the Empyrean by the Warp Storm and effectively scattered throughout space and time. To the great frustration of the Dark Angels, there is no full list or account of who or how many had heeded the dark whispers of the Ruinous Powers and turned against their brothers.Caliban itself broke up under the strain, until all that remained was a small portion of the world that hosted the ruins of the Dark Angels' primary fortress-monastery. The Dark Angels would reclaim this fortress and transform it into a mobile fortress-monastery and a sophisticated work of Imperial engineering known as The Rock.These events remain a secret to all in the Imperium save for the Inner Circle of the current Dark Angels, the leaders of their Unforgiven Successor Chapters and the Emperor of Mankind encased within his Golden Throne.Even within the Chapters themselves very few battle-brothers know the full story. It is only when Dark Angels and Astartes of the Unforgiven Chapters gain entry into their Chapter's Deathwing Company that they learn that many of the Fallen Angels who followed Luther are still alive.