The Lore Explainer – The Codex Astartes

In The Lore Explainer, we take a deep look at the lore behind our favorite games, movies, and books, and talk about the story behind them and sum up what you need to know and how you can find out more. Today we’re talking about the lore behind the Codex Astartes.

The Horus Heresy, the largest and most significant event in 40k lore, tore the fledgling Imperium in two, seeing fully half of the space marine legions turn traitor, following Horus in his rebellion. Ultimately the arch-traitor was defeated, but only at the cost of millions of lives and ultimately that of the Emperor himself.

In the wake of the galactic civil war the survivors were left to pick up the pieces. Following the Emperor’s death the Primarch of the Ultramarines, Roboute Guilliman, was named Imperial Regent, largely marking him as the highest authority in the Imperium (second only to the Emperor). One of Guilliman’s first orders of business was to change the way the Space Marine legions operated, in part to ensure that mankind’s most potent military forces could not repeat the rebellion of the heresy. In order to accomplish this, Guilliman authored a text on the organization of space marine forces called The Codex Astartes.

The Codex Astartes is a tome of military organization which outlines Guilliman’s ideals for how a space marine force should act – how it should fight, organize itself into ranks, and how it should mark its squads and companies. The Codex Astartes dictated that space marine legions be broken into Chapters, groups of roughly one thousand warriors each. Each of these chapters would then be organized into ten companies of one hundred men, split across ten to twenty squads, each numbering five or ten warriors, depending on their tactical focus.

Crimson Fists Primaris Lieutenant with Power Fist
Credit: Alfredo Ramirez

The Second Founding

The most important dictate of the Codex Astartes was the reorganization of Space Marine legions into the much smaller Chapters. These would be drawn from the remaining warriors of the original nine loyalist legions, in a process called The Second Founding. One chapter would bear the name of its original legion and retain its heraldry, and home world, while the others would take new names and find new worlds to draw from, spreading out across the Imperium to better protect it from threats far and wide. Each chapter was responsible for its own recruiting and wargear and would be led by a Chapter Master who was largely independent, reporting only to the Emperor (primarchs would only retain direct control of their named Chapters). This is basically the 40k equivalent of creating expansion teams using a supplemental draft.

Ultimately the plan was to prevent a single general – even a primarch – from commanding tens of thousands of marines, and in this Guilliman succeeded. Chapters were small but flexible forces, and in time each developed their own history and traditions. When the traitor legions made their play, they first had to purge those among their ranks who would remain loyal. Had those forces been separate, standalone forces, they might have had a fighting chance. Under the Codex Astartes, marines would transform from “a horde under a warlord” into a series of independent strike forces capable of acting independently.

The genetic banks used to create marines was moved to a facility on Terra, so that the Adeptus Terra would be responsible for creating and destroying Space Marine Chapters. In the ten millennia since the Second Founding there have been many more foundings, each time creating new chapters – some with more success than others.

They shall be pure of heart and strong of body, unsullied by doubt and untainted by self-aggrandizement. They will be bright stars in the firmament of battle. Angels of death whose swift wings bring extermination to the enemies of man. So it shall be for a thousand times a thousand years, unto the end of eternity and the extinction of mortal flesh.

– Roboute Guilliman

Opposition to the Codex

Not everyone was on board with the Codex Astartes and the breaking of their legions into chapters. Dividing the marine legions would scatter their power, and reduce their effectiveness with regard to defending the Imperium. These disparate Chapters might also come into conflict with each other, when their goals and motivations differ. Reactions to the Codex Astartes among Primarchs were mixed. While Jaghatai Khan and Corvux Corax agreed with the decree and went along with it, Vulkan, Leman Russ, and Rogal Dorn opposed it, with the former receiving an exemption due to the Salamanders having been reduced to so small a force already during the Heresy. Russ and Dorn opposed the order almost to the point of creating a second schism, only relenting after realizing how much damage another internal conflict would cause.

Ultimately Dorn’s defeat at the Iron Cage would see the Imperial Fists’ numbers reduced to the point where they could only be divided into three chapters – The Imperial Fists, Crimson Fists, and Black Templars. Meanwhile the Space Wolves were split into thirteen “great companies,” each the size of a chapter in strength but ultimately leaving the Space Wolves more or less able to operate at legion size if they needed to.

Chapter Organization (Pre-Indomitus)

Under the Codex Astartes, Space Marine Chapters number 1,000 warriors (give or take) and are led by a Chapter Master. These warriors are organized into ten companies of 100 Space Marines each, plus a captain, apothecary, standard bearer, and chaplain for each company. Outside of these structures, chapters also host a number of specialists, including techmarines, librarians, and a fleet, plus a bunch of servitors and human serfs.

Chapters which follow this structure are called Codex-compliant chapters. In a Codex-Compliant chapter, each company in the Chapter has a special function and is led by a Captain, who may also have a special role in the chapter.

1st – Veteran Company

The first company of a chapter consists of squads of veterans, and includes the chapter’s Terminator squads. The company is supported by Land Raiders and Venerable Dreadnoughts, and these forces are generally marked by white markings – white shoulder pad trim and white helmets. The captain of the first company typically serves as the Chapter Master’s second in command and will be responsible for managing the chapter’s fortress-monastery.

2nd, 3rd, 4th, and 5th – Battle Companies

The second, third, and fourth companies are known as battle companies. These share a tactical organization, and consist of:

  • 6 Tactical Squads
  • 2 Assault Squads, which can be deployed as bike squadrons or land speeders
  • 2 Devastator Squads

These companies are supported by Rhinos, Razorbacks, and Dreadnoughts. Note that a company may also have a Command Squad, a group of veterans who act as bodyguards to officers and specialists such as the company captain or a techmarine.

  • The second company of a chapter is marked by either gold or yellow trim, depending on the chapter and which edition of the game you’re looking at. Traditionally the Captain of the 2nd company is also designated the Master of the Watch, and is tasked with the defense of the chapter’s fortress-monastery, though the company charged with that defense may rotate.
  • The third company uses red trim. The captain of the third company is typically designated the Master of the Arsenal, placed in charge of the chapter’s arsenal and munitions.
  • The fourth company uses green trim. The captain of the fourth company is typically also the Master of The Fleet, who serves as the Chapter’s fleet admiral, and commands its flagship and space assets.
  • The fifth company uses grey or dark brown trim. The captain of the 5th company is typically designated the Master of the Marches, responsible for overseeing the deployment of the chapter’s fighting strength. Basically, the chapter’s logistics experts.

6th, 7th, 8th, and 9th – Reserve Companies

Each of the remaining companies has a more focused role, typically only featuring a single squad type.

  • The sixth company consists entirely of Tactical Squads but may be deployed entirely on assault bikes. They typically have orange trim. The captain of the sixth company is typically designated the Master of the Rites, responsible for overseeing all the rites and important rituals of the Chapter cult.
  • The seventh company consists entirely of Tactical Squads but may be deployed entirely on land speeders. They typically have purple or magenta trim. The captain of the 7th company is typically also designated the Chief Victualler, responsible for the chapter’s non-armament provisions. They manage food and also the chapter’s serfs and servitors.
  • The eighth company consists entire of Assault Squads, and may be deployed on bikes or land speeders. They traditionally use light grey trim. Their captain is designated the Lord Executioner, which sounds metal as hell. They’re not really responsible for anything other than killing, which they do very efficiently.
  • The ninth company of a chapter is the Devastator company – composed entirely of Devastator squads, and is marked by light blue trim. The captain of the 9th company is typically designated The Master of Relics and is charged with the care of the chapter’s relics.
  • The tenth company is the Scout company, and is marked by darker blue trim, or no trim. This company is made up of recruits still undergoing the process to become space marines, and as such may not be 100-strong warriors, depending on how recruitment goes for the chapter. These warriors tend to be lightly armed and used as reconnaissance or guerilla fighters, and may make use of scout bikes. The captain of the 10th company is the Master of Recruits, and is responsible for training the chapter’s neophytes.


When Roboute Guilliman was roused from his slumber about ten thousand years later and in the 41st millennium, he took a good, long look at the Space Marine chapters and said “cool, let’s mix things up a bit.” Seeing the need to reinforce chapters against larger looming threats, both internal and external, he made alterations to the Codex Astartes, and did so alongside the introduction of new Primaris Space Marines, who were larger and more genetically and technologically advanced than regular Space Marines.

Under this new organization, Chapters still number one thousand warriors, but companies may include two lieutenants to help lead a company and a company may be made of twenty squads of five marines instead of 10×10. The second through fifth companies are still battle companies, but may be supported now by the reserve companies. And those reserve companies have new names, mostly just to reflect the fact that they have different squads in them with primaris marines and aren’t just tactical/assault/devastator squads.

The tenth company is where the biggest changes happened, with chapters now holding a standard force of ten Vanguard squads in their tenth company in addition to scouts and neophytes. The rate of recruitment was also not fixed, so tenth companies can be much larger, depending on chapter recruitment rates.

Final Thoughts

Since it was originally written, the Codex Astartes had become revered as a holy text to many marine chapters, who felt that its words were sacred law. This was much to the chagrin of the resurrected Roboute Guilliman, who felt they were more like guidelines and not ironclad doctrine. While most chapters in subsequent foundings were made from the Ultramarines’ gene-stock and favored the Codex Astartes’ heraldry, chapters like the Space Wolves, Blood Angels, Dark Angels, and Deathwatch do not and opt for their own structures. Meanwhile chapters like the White Scars adhere to the Codex Astartes but add their own flavor.

As a player, you’re more than empowered to choose whether to follow the Codex Astartes, and really the lore here is more about adding flavor to your chapter’s color scheme with the specific splash of color you want to use for shoulder pad trim. And while there’s something to be said for rigid adherence to the Codex Astartes for a modeling project, if you want to do your own thing, that’s cool too.

Have any questions or feedback? Have a topic you’d like us to cover in a future Lore Explainer? Drop us a note in the comments below or email us at