Tylos Rubio - Horus Heresy: During the opening days of the terrible conflict that would become known as the Horus Heresy in later years, the Warmaster Horus launched his treacherous attack on the world of Istvaan III against the Loyalist elements within four of the Space Marine Legions that had repudiated their oaths to the Emperor and turned to Chaos, including the Sons of Horus, the Emperor's Children, the World Eaters and the Death Guard.Having successfully purged the remaining Loyalists from the Traitor Legions, Horus plotted the next stages of his insurrection against his once-beloved father, the Emperor of Mankind. When word reached Terra of the Warmaster’s treachery at Istvaan III, as a result of the flight of the frigate Eisenstein under the command of Battle-Captain Nathaniel Garro and a small group of Loyalist Space Marines from the Death Guard Legion, the Emperor ordered the deployment of 7 Loyalist Astartes Legions to the Istvaan System to bring Horus to account for his actions.It was while Horus made his plans for what would become known as the Drop Site Massacre on Istvaan V, that the Warmaster sent word to the XVIIth Legion's Primarch Lorgar that the time had come for his Astartes, the Word Bearers, to strike against the Imperium. The Warmaster was keenly aware of the bitter hatred that Lorgar had for his brother Primarch Roboute Guilliman and his XIIIth Legion, the Ultramarines, who had once humiliated the Word Bearers by destroying their city of Monarchia on the world of Khur at the Emperor's orders during the Great Crusade.Horus told Lorgar that he had fed Guilliman false intelligence in regard to a possible threat in the Segmentum Tempestus, far to the galactic south of Terra that stemmed from the Orks of the Ghaslakh Empire. Horus had ordered the XIIIth and the XVIIth Legions to muster and meet at the world of Calth in the Ultramarines' Realm of Ultramar, in order to conduct a massive joint campaign of extermination against the Ghaslakh xenohold, a common mission for the Astartes during the final days of the Great Crusade.It was at Calth that Lorgar launched a surprise attack on the Ultramarines whilst they were gathered for the campaign against the Orks of Ghaslakh that would never begin. The XIIIth Legion was caught completely unaware while the Word Bearers seized the advantage of surprise to completely annihilate their hated rivals. This treacherous campaign came to be known as the Battle of Calth or the Calth Atrocity.There were many portents of the tragedy soon to unfold upon Calth. Given the extraordinary thoroughness with which the XIIIth Legion maintained its readiness, it might have been considered tragic, or incompetent, that so few were heeded. Before the attack on Calth, those gifted with psychic abilities suffered severe headaches and pain behind the eyes. One such gifted individual was Tylos Rubio. He ignored the mysterious pain, chalking it up to nothing more than fatigue after having gone without rest for several days during the preparation phase for the coming campaign against the Orks.It had not been possible to shut down higher mental functions and sleep, or at least remedially meditate, a common form of rest for the genetically-engineered Astartes. This mysterious pain was actually a warning sign broadcast through the Warp of the impending approach of the Forces of Chaos. But Rubio and all of his former Librarian comrades ignored the headaches. Few would survive the coming assault long enough to regret it.