Alpharius Omegon - Horus Heresy: It has long been supposed that since Alpharius was only familiar with one other primarch, Horus, it was self-explanatory why he chose the side he did at the outset of the Horus Heresy. Indeed, the very plan at Istvaan V where Horus struck his first blow against the Loyalist Space Marine Legions by destroying most of the Iron Hands, Raven Guard and Salamanders Legions in a massive ambush, was very reminiscent of plans that Alpharius had created in the past. However, it is possible that there is another reason for Alpharius leading his Legion to the side of the Traitors, a secret known only inside the Legion.Approximately two Terran years before the beginning of the Heresy, during the Compliance of Nurth, Alpharius Omegon was apparently contacted by members of a xenos organisation led by the Eldar but comprising an alliance of individuals drawn from a host of different intelligent species, called the Cabal, who brought to him visions of the impending civil war within the Imperium, and expanded knowledge of the nature and designs of the Ruinous Powers of Chaos. It is believed that the Cabal convinced Alpharius Omegon that the only way to permanently defeat Chaos in the galaxy was to ensure that Horus was victorious in his rebellion against the Emperor. It is perhaps for this reason that Alpharius Omegon, secretly true to the Imperium and loyal to the Emperor, may have chosen to join the Traitors who swore their souls to Chaos.The Cabal, through its only known human agent the Perpetual John Grammaticus, explained that they had foreseen two possible outcomes to the coming Heresy. The first vision had the Alpha Legion remaining loyal to the Emperor and fighting against Horus, ending in the Emperor's victory. However, the Emperor would be gravely wounded and entombed inside the cybernetic sarcophagus of the Golden Throne, neither alive nor dead and no longer able to actively guide humanity. Ten millennia would pass and the Imperium of Man would be fated to slowly decay, until ultimately Chaos would return resurgent and defeat Mankind, condemning humanity to eventual extinction.The second outcome had the Alpha Legion joining forces with Horus and Chaos Undivided and fighting the Emperor. In this vision, Horus was victorious and slew the Emperor. The Traitor Legions would defeat the Loyalists and Terra would belong to Horus, now the greatest Daemon Prince of Chaos. The vision continued with Horus, after slaying his father, shocked into sanity by his conscience and violently freed from Chaos' corrupt hold over him. Disgusted with himself and loathing what he had done, Horus would seek to exterminate the Chaos-corrupted human race in a vast orgy of bloodshed which would consume the entire Imperium in a single Terran century. Though humanity would become extinct, the Chaos Powers would also be destroyed by the destruction of Mankind, since ultimately their existence largely depended upon the collective psychic emanations of humanity in the Warp.The Cabal, an alliance of xenos, Eldar, and a somewhat unwilling human psyker named John Grammaticus, burdened the Alpha Legion with these two visions which they promised would come to pass. The Alpha Legion were told the fate of the entire galaxy rested upon their Legion's decision alone. The Cabal had no time to reach or to attempt to convince another of the Space Marine Legions of what was to come. Either the Alpha Legion ensured the human race died in a century of incredible violence, sparing the other races of the galaxy, present and future, from Chaos forever, or they ensured the human race and the Imperium lived on for ten thousand more years of bloodshed and decay, dooming the entire galaxy to brutal war and the eventual triumph of Chaos.The Alpha Legion decided to join Horus' rebellion and made the decision that they believed the Emperor would have chosen, to sacrifice humanity for the ultimate eradication of Chaos from the universe. Yet their sacrifice seems to have been made in vain, as Horus did not find victory and the Imperium persevered despite the Alpha Legion's decision to support Chaos. This can only lead one to wonder if the Cabal and their future predictions were wrong, if the Cabal secretly served the interests of Chaos and lied to Alpharius simply to corrupt yet another Astartes Legion or if something else occurred that has yet to be discovered.It is noteworthy to mention that John Grammaticus, the human agent who made first contact with the Alpha Legion on the Cabal's behalf, was a man similar in some ways to the Emperor Himself. Grammaticus was a powerful mutant psyker known as a Perpetual who had been alive for thousands of Terran years, and had even met the Emperor face to face once, before the Emperor had finished uniting the various factions of men on Terra during the Unification Wars of the mid-30th Millennium.The actions of the twin primarchs during the Heresy proper are more than vague. Like other Legions and especially the Word Bearers, the many encounters with the Alpha Legion across several sectors and Segmentae revealed that the XXth Legion had secretly built up their strength and was acting on different levels and in different warzones. It would then be logical to assume that both primarchs would increasingly operate separately.