Space Marine Legions
Race	Mankind
Headquarters	Space Marine Legion Homeworlds across the Milky Way Galaxy
Government	Imperium of Man
Leader	Primarchs of each Legion
Military Forces	Twenty Legiones Astartes
Establishment	First Founding (30th Millennium)

The Space Marine Legions (also known as the Legiones Astartes) were the original unit formations of the Space Marines created during the First Founding by the Emperor of Mankind on Terra in the late 30th Millennium. This initial Founding happened before the start of the Great Crusade that reunited the scattered worlds of humanity beneath the banner of the Imperium of Man, while the Unification Wars were still raging on Terra. At the start of the Crusade, as the Legions were placed at the forefront of the Imperial Expeditionary Fleets that left Terra to reunite the human-settled galaxy, the Astartes were renamed Space Marines and their formations the Space Marine Legions. Unlike the current Adeptus Astartes, who serve as a planetary assault and rapid strike force, the Space Marine Legions were the primary frontline military forces of the ancient Imperium of Man. This role changed after the Second Founding, when the Imperial Guard replaced the Legiones Astartes as the Imperium's frontline armed forces, relegating the much smaller Space Marine Chapters to a more specialised role.

Legiones Astartes

A Space Marine Legion was a frontline force of shock-infantry comprising tens of thousands of Astartes warriors armed and equipped with the finest wargear the Imperium could supply. A Space Marine Legion, unlike the 1,000-man Chapters of the present-day Adeptus Astartes created after the Second Founding at the end of the Horus Heresy, could number anywhere from 10,000 to more than 250,000 Space Marines, as well as the Legion's associated Imperial Army, logistical support forces and fleet elements. A force of a hundred of these genetically and biochemically-enhanced super warriors could quell a rebellious city in hours. Thousands could conquer worlds in days, and tens of thousands and even hundreds of thousands wielded at once were the doom of entire species, capable of reducing entire civilisations to mere dust and memory in a span no greater than the single course of Terra's orbit around the Sun.

Founded amid the bloodshed of the Unification Wars of Terra that swept the Emperor of Mankind to dominion over the cradle of humanity, the original military formation of the Legions was the division of twenty numbered units of enhanced warriors, organised very much along the lines of the Thunder Regiments that proceeded them in the Emperor's service and who they would eventually entirely replace. Much of the discipline and organisation of the early Astartes Legions owed greatly to the ancient and proven Terran patterns of strategy, hierarchy and functions as laid down in the revered texts of the Principia Belicosa of Roma and Krom's fragmentary New Model that had survived in the hands of the tyrants of Old Earth down the blood-stained generations of the Age of Strife. To these venerable treatises the Emperor and his commanders had added their own genius and created a sturdy but adaptable strategic framework that spoke to the fundamental strengths and superhuman abilities of the Legionaries themselves. At the outset of the Great Crusade in circa 800.M30, many of these early Legions were organised along the so-called "Terran Pattern" of organisation as formulated by the Imperial Officio Militaris.

Of the twenty original Space Marine Legions, eighteen would survive to grow into vast forces by the end of the Great Crusade in the early 31st Millennium; as for those that did not (the II and XI Legions), nothing can be said in current Imperial records. Nine of these Legions would continue to stay utterly loyal and faithful to the Emperor of Mankind during the Horus Heresy and thus they serve as the genetic forbears of all current Loyalist Space Marine Chapters in the present era. The Space Marine Legions and their Primarchs were the Emperor's primary military forces and most important advisers, respectively, and were intended to be the political and military speartip of the Great Crusade. However, the Emperor also wanted to create a civilian government for the Imperium of Man which would ultimately hold authority over even the Primarchs, a change embodied in the creation of the Council of Terra in the early 31st Millennium that angered many of the Emperor's sons and ultimately became one of the contributing factors to the outbreak of the Horus Heresy. The Legions were aided by the ground and naval forces of the Imperial Army, the predecessor of the present-day Imperial Guard and Imperial Navy, but these forces more often served in support and garrison duties while the heaviest combat and the most important and difficult missions were always carried out by the Astartes Legions.

As the Great Crusade continued the expansion of the nascent Imperium into the galaxy, the discovery of the Primarchs and their newly adopted homeworlds helped to stem an impending crisis that was not widely known of at the time outside of the exalted ranks of the Imperium's ruling War Council: namely, the diminishing stability of the gene-seed itself through over-use and the increasing need for ever greater numbers of Space Marines in the field. This was a matter that only worsened as the Great Crusade pushed ever wider afield into the galaxy. Imperial forces could no longer be concentrated as easily as before, and attrition was taking its toll as years of near-constant battle became decades. To relent the pace of the Great Crusade's progress was for the Emperor simply not an option and so the simple truth was that more Space Marines were needed and they needed to be created faster than before.

A secret conclave of gene-wrights under the Emperor's direct supervision posited the solution that became known as Grabiya's Theorem, which demonstrated that a Primarch's genetic code could be used to stabilise and expand Astartes gene-seed stocks with what was hoped to be "minimal deviation." Alongside this accelerated gene-culturing technique, other previously unavailable genetic technologies were put into effect, reducing the processing time required to create a battle-worthy Space Marine to a single Terran year in some cases. Such accelerated gene-seed techniques, along with absent, inadequate or over-forceful psycho-doctrination techniques, were later found to have unseen fundamental flaws. Many Imperial savants since have come to believe that the drive to create larger Space Marine Legions at accelerated speed played a prime role in the degradation of the sanity and psychological make-up of certain Legions and paved the way for the horror that was to come.

Nine of the twenty original Space Marine Legions chose to follow the Warmaster Horus and pledge their lives and service to Chaos. They became the Traitor Legions of Chaos Space Marines that still threaten the Imperium today. In the end, the Horus Heresy made clear that no single commander could be trusted to wield the enormous power of a Space Marine Legion, never mind several at once. The Ultramarines' Primarch Roboute Guilliman led the Post-Heresy Reformation of the Imperium (the so-called Imperium Secundus) that reshaped the Space Marine Legions into the Adeptus Astartes and broke up each of the remaining Loyalist Space Marine Legions into the myriad 1,000-man Space Marine Chapters to protect humanity from the rise of another Horus.

The remaining two Legions and their Primarchs were lost to the Imperium sometime before the Horus Heresy, with no trace of them remaining. It has been suggested that they were destroyed by, or under direct order, of the Emperor for some unknown, grave transgression, or flaw in their gene-stock, and all evidence of their existence purged from Imperial records.

Legion Size

The Legions were massive armies, and the size of each could vary tremendously. A precise, pre-set formation was never truly achieved or maintained. Even during the Great Crusade some Legions were very large, while others were not. The size of each Legion was fluid, with the numbers of combat-ready Astartes dependent on the number of new recruits, the inevitable battle-losses, the availability of potential recruits, and the administrative skills of the Primarch and his officers.

The largest of all the Space Marine Legions were the Ultramarines, followed by the Word Bearers. The Ultramarines numbered approximately 250,000 Astartes at their peak before the Battle of Calth and the Word Bearers numbered approximately 100,000. It was the Ultramarines' sheer size, as well as the purity of their gene-seed, which insured that more Second Founding Successor Chapters were created from the XIII Legion than from any of the other Loyalist Legions.

The Thousand Sons Legion of Magnus the Red was most likely the smallest of the Astartes Legions as many of the Space Marines within its ranks had developed rampant mutations or uncontrollable levels of psychic powers and had to be granted the Emperor's Peace. The Primarch Fulgrim's gene-samples had been largely lost on Terra making it difficult to develop new gene-seed for his Legion, and this meant that the Emperor's Children found it difficult to recruit new Astartes, also leaving it with a relatively small number of Space Marines. Both of these Legions would increase their numbers to acceptable standards only after their Primarchs were found by the Emperor during the course of the Great Crusade.

Legion Organisation

The smallest formation within the "Logos Terra Militia" and therefore within the early Space Marine Legions was the squad. This consisted of a group of Legionaries under the command of a non-commissioned officer with the rank of Sergeant. Squads varied widely in both size and specialisation, with the majority of the units ranging between 10 to 20 Space Marines. Conversely, very specialised squads such as reconnaissance units or those that might have suffered heavy casualties, might only consist of a handful of Space Marines in active service. The chain-of-command was simple and direct, and the Legions' officers, themselves mighty warriors, would lead their Astartes into battle personally as had long been the wont of the techno-barbarian tribes of Old Earth, and the battle would be taken always to their enemy because to defeat a foe was never enough for the Legiones Astartes, only the utter destruction of an enemy of the Emperor counted as a victory. This cold logic, coupled with their inhuman strength and bearing, and the sheer dread they inflicted on friend and enemy alike, was to give the Space Marines one of their earliest appellations, and perhaps their most appropriate -- "the Angels of Death." It would be a name they would earn time and time again.

Legion Integration and Development

The Legions of the Great Crusade were a fusion of dual natures. They were the product of the Emperor's conquest of Terra and the Sol System. Selected from Terran stock and moulded by the wars of the nascent Imperium, these Legions held a certain commonality of character. A sense of unity and an almost familial bond pervaded their ranks. Given that they were all of the first generation of Astartes, born of Terra, they shared the imprint of their genetic forging and warlike history, and it is no surprise that members of the Legions regarded each other as siblings, as brothers-in-arms. Training, indoctrination and the shared experience of battle reinforced this belief within the Legiones Astartes, encouraging the idea that they were a family born in the cradle of war. This bond of brotherhood would survive as the Imperium grew, but perhaps it was never as strong as it was when the Legions first conquered techno-barbarians under the Terran sun.

The second face of each Legion was that of the people and cultures which had flourished under different stars. As the war to unify Terra became a crusade to conquer the galaxy the Legions grew. Casualties had to be replaced, and as the wars grew in scale so too did the number of losses and the number of recruits that were needed to take the places of the fallen. Initially intakes were drawn from Luna, Saturn's stations, the Proximal worlds, and dozens of others of the near Segmentum Solar fed the Legions' needs for warrior stock. As this occurred the Terran foundations of each Legion became diluted but was never overwhelmed, for the warrior tribes and cultures of ancient Earth were many and their commitment to the Great Crusade resolute.

With the re-discovery of the Primarchs and in many cases newly adopted homeworlds used as Legion fiefs (most commonly the worlds upon which a Legion's new master had been found), this was to change the character of the Legions profoundly. Some alterations were superficial: a habit of speech, a change in close-quarter tactics, martial traditions and warranted additions to iconography and even language. But for others the change would prove dramatic, with entire paradigms of culture, tradition and even ideology overwriting what had come before, such as in what came to be known as the Space Wolves and Dark Angels Legions. In many cases the stamp of the Legions and the will of the Primarchs on their recruits came to largely outweigh differences of birth or blood, but in other Legions such as the Luna Wolves and the Emperor's Children, a subtle divide would grow between those veterans who had been recruited into the ranks of the Astartes by the Emperor from Terra and those who had come into the Legion from their Primarch's homeworld. This rift would be one factor among many that would lead several of the First Founding Legions towards ultimate damnation.

By the middle years of the Great Crusade the ongoing effects of these shifts within the Legions had resulted in a wide disparity in culture and organisation between them. The outward sign of this was the development of distinct character which meant the original Terran military patterns they had adhered to at the outset of the Great Crusade had been largely abandoned or become so modified and diluted as to be in some cases unrecognisable. There were, of course, exceptions in whole or in part, such as could be found within the Ultramarines and Iron Warriors Legions who built upon rather than abandoned what had gone before, as well as those such as the White Scars to who the strictures and precepts laid out by the Officio Militaris were no longer even notionally applied. There are those that have cited this increasing idiosyncrasy in hindsight as the seeds of division, of a sense of insularity and "otherness" growing between one Legion and another. This itself only fuelled rivalries and feuds that had begun to simmer beneath the surface of the Great Crusade, both between the Primarchs and their Legions, that would later be exploited by Horus and his heretical conspiracy, and lay them open to the introduction of the Davinite warrior lodge cult structures into those Legions he favoured. These warrior lodges were the avenue by which the stain of the Warp would taint those Legions that turned Traitor.

Legion Structure

By the time of the outbreak of inter-Legionary hostilities during the Istvaan III Atrocity, the command and organisational structure of a Space Marine Legion was often more a mirror of the character and preferences of its Primarch and its abiding culture than formal writ. While certain formations and features were common as an outgrowth of practical manners such as deployment and logistics, their organisation and use was far from standardised. During the Great Crusade there were numerous terms for the internal constituent units of a Space Marine Legion, from largest to smallest: Great Companies, Regiments, Chapters, Battalions, Cohorts, Demi-Chapters, Companies, Squads and Maniples. Most often, the practical reality of their disposition would vary still more as terminology used within different Legions for equivalent ranks and specialisations bore the mark of the Legion's character rather than the desires of the Imperium's central administrators for a common nomenclature. In some cases this discrepancy increased as local languages and dialects such as Fenrisian or Khal'd had come to replace Imperial Terran (the forerunner of High Gothic). With these caveats in mind, the Strategic Disposition of a Space Marine Legion chart above describes the broad and most common structural basis of an Astartes Legion (as well as some of the more commonly used terminology of rank) in the latter half of the Great Crusade.

Generic Space Marine Legion Order of Battle

By the time of the middle years of the Great Crusade, there was great variation in each Space Marine Legion's order of battle and size. However, in the most generalised sense, a Space Marine Legion was a force comprised of approximately 11 or more smaller sub-units known as Chapters, each subsequently further divided into a deep hierarchy of smaller sub-units led by officers whose rank terminology often differed from Legion to Legion. The order of battle presented here should be considered generic and to be superseded by the more specific structure and rank terminology of a given Legion, if such information is available within current Imperial records.

• Legion Command: Primarch or Legion Master (if the Legion's Primarch had not been rediscovered)
  • Praetorate or Ancients of the Legion (Senior Staff Officer Cadre)
    • Consular Representatives [Senior representatives of the Armourium, Astropathic Chamber, Navigators-Plenipotentiary, Librarus (if present in Legion), Apothecarion, Masters of the Fleet, Castrum of Ordnance, Castellans of Domain, et al]
    • Vexillarius (Legion Standard Bearers, Subalterns and Equerries)
    • Honour Guard (Praetorian Bodyguard Formations for Primarch -- number and structure varied by Legion)
    • Legion Assets:
      • Planetary Domains
      • Capital Class Warships
      • Secondary Escort Squadrons
      • Legion Armourium
      • Legion Apothecarion
      • Legion Librarus (if present in Legion)
      • Auxiliary Forces (Non-Space Marine, usually Imperial Army)
      • Legion Support Corps (Victuallers, Commissary, Legion Serfs, Indentures, Servitors, etc.)
• Chapter I (Chapters were alternatively designated as Great Companies, Harrows, Millennials, etc.)
  • Originally each Chapter was composed of roughly 1,000 line Legionaries, but as the Legions grew, this number began to vary substantially by Legion, and also through the vicissitudes of war and the availability of replacement recruits
• Chapter II
• Chapter III
• Chapter IV
  • Battalion I (Battalions were alternatively designated as Cohorts, Regiments, Battle Groups, etc.)
    • Battalion Command (Example): Lieutenant Commander (alternatively designated as Commander, First Captain, Shadow Captain, Marshal, Legate, etc.)
      • Battalion Consuls (Senior Specialists and Advisors)
        • Battalion Vexillarius (Standard Bearers, Subalterns and Equerries)
        • Battalion Command Bodyguard
        • Battalion Assets:
          • Strike Cruisers
          • Navigators Ordinary
          • Drop Pods and Rams
          • Light Gunship Squadrons
          • Super-heavy Detachments
          • Skimmer Strike Detachments
          • Support Artillery Detachments
          • Techmarine Covenants
          • Apothecarion Sections
          • Dreadnought Talons
          • Reconnaissance Sections
        • Company I (Companies were alternatively designated as Maniples, Bands, Brotherhoods, etc.)
          • Nominally Battalions numbered five companies, each of a hundred Legionaries -- Company I was composed of Veterans and other elite units, II, III and IV were line companies and the V Company was comprised entirely of specialist troops such as dedicated Assault, Outrider or Destroyer units. However, in practice many larger Legions regularly exceeded this number of companies, maintaining battalions with seven or ten companies each folded under a particular command, while individual companies also varied in strength
        • Company II
        • Company III
        • Company IV
        • Company V
          • Company Command (Example): Company Captain (alternatively Centurion, Prime, Wolf Lord, Blooded, etc.)
            • Company Standard Bearer
            • Company Command Bodyguard Squad
            • Company Assets:
              • Heavy Support Squads (5-10 Space Marine Legionaries)
              • Assigned Veteran or Specialist Squads (Various)
              • Gunships
              • Rhino Armoured Transports
              • Tank Detachments
              • Support Weapons Batteries
              • Dreadnoughts
              • Techmarines
              • Apothecaries
            • 1st Lieutenant
              • Lieutenants were the most junior officers of the Legion. They also differed in designations such as Dominar, Decurion, Pack Leader or Chieftain, and in some Legions the numerical positioning of the officer within the Company indicated seniority or ceremonial role and had further titles in rank
              • Tactical Squad (10-20 Space Marine Legionaries)
              • Tactical Squad (10-20 Space Marine Legionaries)
              • Support Squad (5-10 Space Marine Legionaries)
            • 2nd Lieutenant
              • Tactical Squad
              • Tactical Squad
              • Support Squad
            • 3rd Lieutenant
              • Tactical Squad
              • Tactical Squad
              • Support Squad
        • Company VI
        • Company VII (etc.)
  • Battalion II
• Chapter V
• Chapter VI
• Chapter VII
• Chapter VIII
  • Chapter Command (Example): Lord Commander (Alternatively Chapter Master, Khan, Warsmith, Magister, etc.)
    • Chapter Consuls (Senior Specialists and Advisors to the Lord Commander)
      • Chapter Vexillarius (Chapter Standard Bearers, Subalterns and Equerries)
      • Chapter Command Bodyguard
      • Chapter Assets:
        • Chapter Flagship Battle-Barge/Capital Ship
        • Planetary Assault Craft and Drop Ships
        • Escort Squadrons
        • Gunship Squadrons
        • Chapter Armourium
        • Legion Armoured Divisions
      • Battalion I
      • Battalion II
        • Nominally each battalion was composed of five hundred line Legionaries each, as well as various specialists and support staff
• Chapter IX
• Chapter X
• Chapter XI (etc.)

Original Legion Names

The Astartes Legions were for a very long time after their initial creation under the direct command of the Emperor and originally all Astartes recruits were drawn from Terra itself rather than the later Legion homeworlds of the Primarchs. The Terran Space Marines would always remember these early times before their Primarchs were re-discovered and the Legions initially had overwhelmingly Terran cultural traditions and origins. Later, as the Primarchs were found, the new recruits would have very strong loyalties towards them, and some of the Primarchs would re-name their Legions to accord with their own personalities and cultural sensibilities. The Emperor saw no problems with this development; he believed the loyalty of the Primarchs to him was unshakable. This reasoning would be proven to be sadly mistaken; for all their seeming physical and mental perfection they were still human beings and prone to all the sins of humanity, including greed, anger and the lust for power, recognition and advancement -- all emotions that left them susceptible to the temptations offered by the Ruinous Powers of Chaos.

The first Primarch to be found was Horus, rediscovered on the world of Cthonia. He was the Emperor's favorite, and he and his XVI Legion, the Luna Wolves, were granted the honour of being renamed the Sons of Horus following Horus' elevation to the rank of Warmaster, and his survival despite the wound that had nearly killed him on the moon of Davin. The I Legion was given the name Dark Angels by Lion El'Jonson, and the XIV Legion, the Dusk Raiders, had their moniker changed to the Death Guard by Mortarion. While its original name is unknown, the highly honorific name Emperor's Children was awarded by the Emperor to the III Legion only after a speech made by their Primarch Fulgrim so impressed the Emperor of Mankind that he granted that moniker to Fulgrim's Legion. The XII Legion was originally known as the War Hounds by the Emperor before the Primarch Angron renamed them the World Eaters. The XVII Legion, the Imperial Heralds, were renamed the Word Bearers after they were reunited with their highly religious Primarch Lorgar, who tragically intended to bring word of the Emperor's divinity to every world that his Legion brought into Imperial Compliance.

Primarchs and Astartes Legions

Sources

• Codex: Black Templars (4th Edition) p. 20
• Codex: Dark Angels (4th Edition)
• Codex: Space Marines (5th Edition)
• Codex: Space Marines (4th Edition)
• Codex: Ultramarines (2nd Edition)
• Realms of Chaos: Slaves to Darkness, pp. 240-244
• Imperial Armour - The Horus Heresy - Book One: Betrayal, pp. 29-30
• The Horus Heresy: Collected Visions by Alan Merrett, pp. 12-13, 16-21, 24, 27
• White Dwarf 166 (US), "Space Marines: Codex Imperialis Extract - Legions of Adeptus Astartes," pp. 8-19
• White Dwarf 129 (US), "Space Marine Armor: Background," pp. 13-29
• White Dwarf 98 (US), "The Origin of Legiones Astartes" by Rick Priestly, pp. 12-17
• Horus Rising (Novel) by Dan Abnett
• Descent of Angels (Novel) by Michael Scanlon, pp. 235, 303
• The First Heretic (Novel) by Aaron Dembski-Bowden
• Deliverance Lost (Novel) by Gav Thorpe
• Age of Darkness (Anthology) edited by Christian Dunn, "Rules of Engagement" by Graham McNeill
• Know No Fear (Novel) by Dan Abnett
• Angel Exterminatus (Novel) by Graham McNeill
• Soul Drinker (Novel) by Ben Counter
• The Bleeding Chalice (Novel) by Ben Counter
• Warriors of Ultramar (Novel) by Graham McNeill