Alpha Legion - Ghost Legion: Before the vile treachery of Horus came to being, the XXth Legion, its formation, and purpose was shrouded in mystery and bellicose concealment from the rest of the Imperium. This secrecy was colluded -- as is evident -- by the highest circles of power. Indeed, it cannot be doubted that it was the Emperor's will.It is believed by many Imperial scholars that the secrecy surrounding this "outsider" Legion and its designed purposes would later serve to conceal the dark transformation at its heart which was long in its gestation. This malediction and the increasing addiction for its own preternatural use for subterfuge and destruction, only worsened after the ascension of Horus to the rank of Warmaster.The Alpha Legion became a twisting serpentine force of formless shadows, as dangerous and deadly as the multi-headed monster of ancient myth that in latter days became its modus operandi and its icon. It was a weapon neither first the Emperor nor later the Warmaster could control.The pall of mystery surrounding the XXth Legion can be traced back to their creation. The last known of the gene-seed strains used in the creation of the Legiones Astartes at the end of the Unification Wars, factors relating to the XXth Legion were kept beyond the usual secrecy and security that the Emperor chose to surround the Space Marine project with.The XXth along with the XVIIIth (Salamanders) and VIth (Space Wolves) proto-Legions, were formed and established largely in separation from the rest of the Legiones Astartes and were generally thought created to very specific ends and purposes. What plan of the Emperor's lay behind this action cannot now be known, and even at the dawning of the Age of the Imperium, this was one of many secrets the Emperor kept both from the Imperial Court and many of His own advisors, and the primarchs themselves.These Legions were kept veiled and distant from the beginning, breeding distrust between them that, save in the case of the XVIIIth Legion -- who would later become the widely renowned Salamanders Legion -- would never disappear. In the case of the Alpha Legion, it would instead worsen over time. This first mystery would breed others, and questions would continue to go unanswered not simply about the XXth Legion's methods and nature, but about the use to which it was put in its earliest days.Of the early solar decades of the XXth Legion on Terra and during the re-conquest of the Sol System almost nothing can be said with any accuracy whatsoever, and even the cluster of myths and rumours that would later grow to surround the Legion's activities is absent. What remains instead are a few sparse but suggestive fragments, anomalous records of unknown Legiones Astartes units carrying out targeted strikes, abductions and assassinations, both on Terra and beyond, and reports of Space Marine units answering to no known masters or Legion allegiance passing through war zones on high priority missions and under the writ of unassailable clearance codes which broached no question.Rumour and supposition even surrounded the designation "Alpha", which by some records is connected with the XXth proto-Legion from a very early period. This, aside from the numerous occult and arcane associations and significance that certain sources choose to derive from this fact, ties into another, more prosaic, potential association dating back to the hidden work of the Emperor's own gene-labs.It is apparent from numerous extant sources that during their creation, each nascent proto-Legion after the Primus or Ist Legion (later the Angelis Tenebrium or Dark Angels), was raised first to active service in a staged process of testing and trials before the full active force was created through mass recruitment from amongst Terran populations loyal to the Emperor's cause.Each stage of creation would result in expansion of the gene-seed implantation on progressively larger groups of Neophytes. The last of the these preliminary stages was, according to sources, the "Alpha" induction. This was in essence believed to be the first non-experimental implantation, and its purpose was to create a proto-Legion of Astartes at minimum fighting strength to be field-tested in open battle.Tellingly, there is no recorded evidence that the XXth pattern gene-seed group, although having been approved by the Emperor after its limited battle-tests, was ever ordered to expand to full implantation, or received an allotted intake region of Terra for mass recruitment as the rest would do during the early years of the Great Crusade. This then effectively limited the XXth Legion to a body of around 1,000-3,000 Astartes and effectively side-lined them while their contemporaries underwent rapid expansion and deployment through the opening phases of the Great Crusade. The question then remains, why?Almost certainly it was not a question of gene adaptation; the extant sample records place the gene-seed implantation success rate for the XXth pattern as being in the highest end of the recorded spectrum. The evidence would indicate it was certainly far superior to certain other developed types (the difficulties experienced by the VIth (Space Wolves) and IXth (Blood Angels) genetic patterns being documented elsewhere). Likewise, their battlefield performance was stated high, removing the other most obvious likelihood for considering the XXth proto-Legion a failure.There are three outstanding theories that have been posited as to why the XXth Legion was not apparently expanded to full Legion strength during the early Great Crusade which may each have some merit. The first is entirely mundane, and is simply the sabotage of suitable manpower. The recruitment assignments of the other Legions during the period now covered most of the suitable genetic and cultural candidates of both Terra and the Sol System, and some sort of disaster (which has been redacted from official Imperial records) had proven the folly of attempting to recruit Legiones Astartes stock from potentially tainted sources.The second is the suspicion that some hidden problems, or potential flaw had been discovered which prevented the proto-Legion's expansion -- although this in many ways seems unlikely for it is to suggest the Emperor was either unable or unwilling to solve such a problem and equally unwilling to ruthlessly eradicate a failed experiment as He had done before.The third theory is that the XXth Legion was deliberately preserved separately as an isolated unit for other specific or military reasons possibly to act as a strategic gene-seed reserve or indeed a control group as some have suggested. This theory also posits the possibility that the XXth proto-Legion was held back to undergo some further development and conditioning unique to them that the rest of the Legiones Astartes was restricted from by design. There remains evidence that this last "Alpha"-stage Legion of the Emperor led to the later development and eventual creation of his personal cadre of transhuman protectors, the Legio Custodes.