First Founding
- "They shall be my finest warriors, these men who give of themselves to me. Like clay I shall mould them, and in the furnace of war forge them. They will be of iron will and steely muscle. In great armour shall I clad them and with the mightiest guns will they be armed. They will be untouched by plague or disease, no sickness will blight them. They will have tactics, strategies and machines so that no foe can best them in battle. They are my bulwark against the Terror. They are the Defenders of Humanity. They are my Space Marines and they shall know no fear."
- --The Emperor of Mankind on the creation of the Adeptus Astartes
After he conquered Terra, the Emperor of Mankind set out on a Great Crusade to re-unite the lost human colonies into a mighty Imperium. He soon realized that bog-standard humans wouldn't be enough; some situations called for a small number of devastatingly powerful warriors, a surgical strike force to smash enemy linchpins. To fill this role, he created his Primarchs, and from their genes, he created the Legiones Astartes, the twenty Space Marine Legions:
| Legion Number | Primarch | Homeworld | Name of the Legion | Allegiance | |
| I | Lion El'Jonson | Caliban | Dark Angels | ||
| II | +++Records expunged+++ | ||||
|---|---|---|---|---|---|
| III | Fulgrim | Chemos | Emperor's Children | Traitor | |
| IV | Perturabo | Olympia | Iron Warriors | Traitor | |
| V | Jaghatai Khan | Chogoris/Mundus Planus | White Scars | Loyal | |
| VI | Leman Russ | Fenris | Space Wolves | Loyal | |
| VII | Rogal Dorn | Terra, Inwit | Imperial Fists | Loyal | |
| VIII | Konrad Curze | Nostramo | Night Lords | Traitor | |
| IX | Sanguinius | Baal | Blood Angels | Loyal | |
| X | Ferrus Manus | Medusa | Iron Hands | Loyal | |
| XI | +++Records expunged+++ | ||||
| XII | Angron | Nuceria, Bodt | World Eaters | Traitor | |
| XIII | Roboute Guilliman | Macragge | Ultramarines | Loyal | |
| XIV | Mortarion | Barbarus | Death Guard | Traitor | |
| XV | Magnus the Red | Prospero | Thousand Sons | Traitor | |
| XVI | Horus Lupercal | Cthonia | Luna Wolves/Sons of Horus | Traitor | |
| XVII | Lorgar Aurelian | Colchis | Word Bearers | Traitor | |
| XVIII | Vulkan | Nocturne | Salamanders | Loyal | |
| XIX | Corvus Corax | Deliverance | Raven Guard | Loyal | |
| XX | Alpharius Omegon | Unknown | Alpha Legion | Traitor/Loyal/Maybe Both | |
Organization
The Legio Astartes, being far larger than current Space Marine Chapters, were organized along drastically different lines. At the head of the Legion was its Primarch Commander who oversaw the Legion's headquarters. Below this were the Chapter of the Legion, each of which was commanded by a Lord Commander. Each Chapter in turn was divided into a number of Battalions led by a Lieutenant Commander. Each battalion was then further divided into Companies led by a Captain. The Company, itself divided into a number of Squads, was the basic military division of the Legio Astartes. Due to the varying sizes of each Legion and the varying nature of supply and attrition, there was no fixed number of how many Chapters, Battalions, Companies, and Squads a Legion would contain. But even then, there was no fixed institution that a particular Company should be composed of certain units, with each Company specialising naturally as marines and officers became veterans of a certain form of warfare.
Number of Legionaries
The Legions were massive armies, and the size of each could vary tremendously. A precise number was never truly achieved and maintained. Even during the Great Crusade, some Legions were very numerous, while others were not. The numbers would always vary with new recruits and inevitable battle-losses, and also important was the availability of potential recruits and the administrative skills of the Primarch and his officers.
The most numerous Legion of all was the Ultramarines. The Thousand Sons of Magnus were of a small number as many of them had developed mutations or uncontrollable levels of psychic powers. Fulgrim's samples had been largely lost, and this left the Legion of the Emperor's Children also with a very small number. Both of these Legions would increase their numbers to acceptable standards only after their Primarchs were found.
The approximate sizes of a few of the Legions at the start of the Heresy have been given in various sources (it should be noted that originally these numbers were much smaller, a full zero knocked off until they were upped by the BL/Forgeworld writers):
- Ultramarines - 270,000+ (They have two double-strength reserve Chapters and Vigil Overseers)
- Word Bearers - 180,000 to 250,000
- Dark Angels - 166,000 to 216,000 and possibly even more (Once, they were considered the largest legion and the single most powerful force of Imperium, however somewhere in 890M30, their numbers fell below 166,000 after they prevented the destruction of the entire northern imperium by an unknown menace from the outer darkness of Milky Way, the Ultramarines overtook them soon after) - Just before the Heresy started Luther who had decided that Caliban should be free of what he saw as the imperium’s tyranny cancelled the Deployment of over 2000 new recruits to the Legion, he would further speed up the process in which new legionaries were being trained so by mid heresy there was around 30,000 new Dark Angels on Caliban who were swearing oaths of fealty not to the Emperor but to Caliban and the Order.(Not everyone was pleased with this especially those who had originated from Terra)
- Iron Warriors - 150,000 to 180,000 and possibly even more - (They also have the largest / most powerful starships)
- Alpha Legion - 90,000 to 130,000(the most average, conservative estimation) to 180,000 and possibly even more. No-one knows for sure - However, some sources are even assuming their actual size is rivaling that of Ultramarines.
- Sons of Horus - 130,000 to 170,000
- World Eaters - 150,000
- Night Lords - Officially 90,000 to 120,000 - in hindsight, their actual size is said to be at least on a par with larger Legions(World Eaters, etc.) with unknown numbers of Legionaries are active across wider Galaxy, prosecuting their own crusade/terror campaigns outside of Imperial territory.
- Blood Angels - 120,000+
- Iron Hands - In excess of 113,000
- Emperor's Children - 110,000
- Imperial Fists - 100,000 - (They also have the single largest fleet in the Imperium, consisting of 1500+ vessels plus the Phalanx)
- Death Guard - 95,000
- Salamanders - 89,000
- Raven Guard - 81,000+ (Several thousands of exiled Legionaries are operating independently at fringes of Galaxy/they are also referred as the smallest of Legions - foreshadowing of expansion of Thousand Sons numbers in possible future?)
- Thousand Sons - 10,000
As you can see, most larger Legions joined traitors(with exception of Ultramarines, Dark Angels and possibly White Scars) and loyalists were considerably outnumbered from the beginning.
Other Legions have not yet been so explicitly numbered, but their impression can still be gained by how they are described.
- Space Wolves - They are mentioned as one of the substantially-sized Legions, directly compared with Luna Wolves and Iron Hands. That means, their actual strength has to be over 100,000 at bare minimum. In fact, they significantly outnumbered defending Thousand Sons at Siege of Prospero.
- White Scars - Fuck knows, in the books Scars/Brotherhood of the Storm, one of the human characters from the Departmento Munitorum is attached to the Legion to figure precisely this out, but finds it practically impossible due to the way that the legion operates. However, considering their semi-autonomous status, far and wide recruitment pool and extremely high-quality gene-seed, their actual size must be quite large - probably on a par with Iron Warriors - (In fact, V Legion was one of the largest Legions along with Primus and IVth Legion at Unification War and early days of Great Crusade and that means something)
Horus Heresy
For all their power, the Space Marines and Primarchs were not perfect; half of them were sufficiently flawed to be tempted by (or driven to) Chaos, led by Warmaster Horus. The traitors were defeated, but at a terrible cost, including the near-death of the God-Emperor of Mankind and trillions of deaths.
Roboute Guilliman decided that the so-called Horus Heresy was proof that one man could not be trusted with power over one-twentieth of the Imperial Armed Forces, so he enacted several reforms to divide the Imperial Army into the Imperial Guard and Navy, and split the remaining loyalist Legions into Chapters, in accordance with his Codex Astartes. This event was later known as the Second Founding.
Legions in 40k
Technically all of the Chaos Marines are still 'legions', at least in name. They never split into chapters so legions they technically remain. However, since they are all split up into roving warbands and there is no central control it's hard to say they really count anymore. Perhaps most importantly it's impossible to guess how many dudes there are even technically in any legions pool. When they aren't fighting the imperium they are fighting each other, and since none of the Black Crusades have been successful we can reasonably assume that marines aren't pouring out of the Eye Of Terror in their hundreds of thousands. It's utterly impossible to guess how many dudes they got. They got some. Probably not that many. Definitely many many many less than they arrived at the Eye with, which was obviously rather fewer than they began the war with.
As for the loyalists... Since the introduction of the Codex Astartes, there are obviously no longer any Space Marine legions though that does not stop certain chapters from being described or implied to be at "Legion Strength". Though this is often a common Neckbeard error and sometimes even gets used in the fluff, where the term is mistakenly used to describe any significantly oversized chapter, though even then they never compare to the forces from the Great Crusade. Though some make a good attempt at it:
- Black Templars are obviously over-strength in multiples of 1000 and keep to the spirit of the great crusade unlike any other chapter. This force is made up of three primary crusade fleets of unknown size which can end up spread over up to thirty engagements, where the size of a force could be as large as "nearly" chapter strength (but not over for obvious reasons) or as small as a single ship and a handful of squads, so can be averaged at around chapter strength for each primary fleet. This arrangement is meant to be fluid, and changes all the time as fleets merge and disperse. Respectable figures put their numbers between 2000-6000
- Space Wolves make no secret of the fact they ignore the Codex Astartes, but even then they are no-where near their original size. In M32 during the Battle of the Fang it is remarked that most of The Aett is actually abandoned. Furthermore, Logan Grimnar's own Great Company numbers 200 marines prior to the Sanctus Reach campaign and is the largest company on its own (ie: not including the chapter assets). Their current number aught to be between 1200-3000.
- Astral Claws were actually accused of Legion building and declared heretics even when they were not yet followers of Chaos, their number at the time of the Badab War was around 3000, though they never even used that number as a single force and spread themselves throughout their PDF forces
- The Unforgiven are most likely one of the closest examples of a true Legion in that each of the successor chapters arrange themselves under one secret command structure (the Inner Circle). Though they each obey the letter, if not the spirit of the Codex Astartes and maintain mostly standard chapters of ten companies. The combined numbers of Dark Angel's successors would put them at around 150,000 marines, and this is just a rough estimate, though we don't know if all of the Dark Angel's successors actually consider themselves part of the Unforgiven. Some definitely do though. Oh yes indeed. The Inner Circle has been known to send a random successor chapter across the galaxy to do the space marine equivalent of getting them a six pack (of traitors) when the main chapter is too busy.
- Ultramarines - Ironically, the ones who uphold the Codex Astartes most strictly are the most hypocritical when it comes to deviations from it. The 23 Second Founding chapters of the Ultramarines are all represented in the senate of Ultramar and look to the Lord of Macragge as their nominal leader. The Ultramarines even keep a SPARE chapter lying around to replenish their own ranks whenever they suffer terrible casualties. Also if certain people had their way then EVERY chapter would answer when the Ultramarines snap their fingers. Because the Ultramarines account for nearly half of the later-founded chapters in the Imperium, they would amount to around 500,000 marines.
- Then again... The thing is that all of the original legions maintain ties with with their subsequent founding legions. Blood Angels occasionally call all their bros together, and last time they did everyone out to the 23rd founding showed up for blood and pancakes. Every now and again every Dorn-descended chapter sends a champion (and his mustache) to a big fighting contest to see who is the Dorniest. Essentially every Legion that wasn't murdered into damn near extinction (ie had enough marines to have many descendants) maintains some tie between them. Ultramar spanned FIVE HUNDRED worlds. That's a lot of worlds. And all of them were tithed to the Ultramarines. Guilliman wanted his boys to be warrior-kings. That meant that he gave worlds to be run by marines, and in the end his ideal was each chapter master and senior captain would be master of a world too and look out for it's population. Sooo... 500 worlds -> 500,000 marines, 1 modern chapter per world, not exactly shocking when you say it like that. And let's not to forget that Ultramar was a republic (In Plato's sense of a republic anyway; ruled by just men (which is different to being ruled just by men by the way) as opposed to democracy specifically). So there is a senate. Because that's what republics have. But the senate isn't something that secretly orders chapters around (*ahem* Dark Angels) it's just what there was around when each chapter master split off into his own chapter instead of being part of the legion. In short - The Ultramarine decedents are bros. They bro it up. They probably bro-fist Papa Smurf since he has the big giant pimp-gloves. I know Matt Ward fucked the reputation of the Ultramarines, but he wrote almost none of their fluff (seriously, he said a bunch of shit outside of canon but other than a few pages here and there in codexes he really hasn't effected all that much, he's just effected how you feel about them which isn't the damn same) and they definitely don't do anything that other 1st founding chapters aren't doing. Except they do it bigger.
Two Unknown Legions
In the First Edition of Warhammer 40,000, the twenty First Founding Chapters were all known. It seems that Games Workshop had more love for some than others; when they made fluff revisions in the transition to Second Edition, the Valedictors and Rainbow Warriors were demoted to one of the "Later Foundings."
Nowadays, nothing concrete is known about the Legions II and XI, and likewise their unknown Primarchs. Officially, the Imperium deleted all records regarding the "Lost Legions"; the only reminder of the two legions were empty plinths in the Hegemon where statues of the Primarchs stood at the Imperial Palace. Throughout the Horus Heresy series, it is suggested that the Space Wolves destroyed them for some reason. The Horus Heresy: Massacre includes a timeline of the events at the end of the Great Crusade, and in 965 and 969.M30, the Space Wolves engaged in two missions from which all data was redacted. In the book The First Heretic, when a daemon takes the Word Bearers on a trip back in time to show them the creation of the Primarchs, the Word Bearers dialogue indicates that the XI Legion in particular did something bad enough for the Emperor to lead their purge himself, and that the left-over Marines were folded into the Ultramarines (their Chaplain dismisses it as a rumor, though it is public record that the Ultramarines received a major boost in troops at the time). In the book Fear To Tread, Sanguinius tells Horus that he hasn't revealed the existence of the Red Thirst to the Emperor because he fears that the Blood Angels would be purged as well, indicating that gene-seed flaws may have also been a factor. Deliverance Lost has a dialogue between taking place during Corax's first meeting with the Emperor where he asks why only sixteen of his brothers were waiting to meet him if he was the nineteenth Primarch to be found, only for the Emperor to deflect the question; consequently, we can assume that the Legions were purged sometime before Corax's discovery (and were never around for the Horus Heresy). He also forced the remaining Primarchs to swear an oath never to speak of their absent brothers, so whatever they did must have been extraordinarily bad. In Legion, a ship's captain notes that the naughtiness of the Alpha Legion isn't the first time that a Legion has "overstepped it's mark" and that the Imperial Army fleet should report the Alpha Legion "before they become too powerful," which might imply that one of the Legions got away with naughtiness for a long time and then used their entire Legion to fight the Emperor. 'Horus Heresy Book 3: Extermination also hints at the fate of the two missing Legions, first hinting that one Legion did not pass the "Alpha" intake (to take them up to Legion-Strength) when going through testing and the other saying that "the disaster of [REDACTED] had proven the folly of attempting to recruit Legiones Astartes stock from potentially tainted sources." These could be in reference to the same Legion (using tainted stock in the Alpha intake) or two separate ones, with Legion A fucking up in the Alpha intake and Legion B using tainted stock in the later Great Crusade.
Since Horus and the other traitor Primarchs managed to keep their records un-expunged during the Horus Heresy (and afterwards, since the Space Wolves clearly know who Magnus is, the Grey Knights clearly know who Mortarion is, and Horus' name seems to have become a swearword), it can be assumed the missing Legions' naughtiness was something even worse. Possibly they refused to wear pauldrons, we don't know.
Or there may simply be no missing Legions. According to a source who allegedly worked for Games Workshop for five years (seen here), Rick Priestley (who helped write the first Rogue Trader) read about the Roman notion of Damnatio Memoriae, and simply threw in the idea of two "missing" Space Marine Legions as a "nod" to Imperial Rome (specifically, the three Roman legions whose numbers were never used after they were wiped out in the disastrous Battle of the Teutoburg Forest. So, nothing significant can ever be revealed about them, because they never really existed in the first place. Except they totally existed in the current canon, even if they started as a joke. Also, the real reason that they were kept around between Rogue Trader and recent revelations was so that people could make up their own pair of Primarchs for model painting and personal fanon (although this has lost its effect as doing so is a step in sending them down the path of the Mary Sue).