40K Lore: Sons of Magnus – After the Heresy

Today Loremasters we speak of the Thousand Sons Legion in the wake of the Wolves’ devastation of their homeworld.

Post Razing of Propero

Having been thus deliberately removed from the board by the machinations of Chaos, the Thousand Sons played no part in the birth of the Horus Heresy. In fact, exactly when and why they chose to ally themselves with Horus and his traitorous rebellion is not clear, although it is believed that their chief motivation was to gain sanctuary and protection from further Imperial attack. Of course, considering how Tzeentch had orchestrated events so far, it is likely that they had little choice in the matter at all.

After their escape from Prospero, the Thousand Sons discovered that – once again – they had been reduced to only around one thousand living members. Their actions during the bulk of the Heresy are not currently known, though a portion of the Legion did engage the Space Wolves at the Battle of Yarant. When Horus’s forces fell on Terra itself some years later, Magnus and the Thousand Sons were with him. Noted to be a very small contingent of the Chaos forces, the Thousand Sons contented themselves with summoning daemonic reinforcements and casting supporting spells rather than engaging in pitched battle for most of the Siege of Terra. However, once the outer walls of the Imperial Palace had been breached, the Thousand Sons found themselves required to break down the final wards and fortifications of the inner palace itself. Advancing to the Ultimate Gate, part of the legion held off Imperial counter-attacks while the senior sorcerers attempted to destroy the defences with psychic power and sorcerous ritual. This assault came to naught however, as a contingent of Imperial Fists led by Rogal Dorn arrived in the combat zone and drove the Thousand Sons off at much the same time as the Emperor himself directed the surviving Librarians of the Blood Angelsand Imperial Fists to block the attacks of the Thousand Sons sorcerers.

The Thousand Sons retreated from Terra after the death of Horus alongside the other Chaos forces, before using their sorcerous powers to open a warp route that would transport their fleet directly to the Planet of Sorcerers.

Post Heresy

The dedication to the Chaos God Tzeentch resulted in several changes to the organisation of the legion, but had little direct effect on their combat doctrine. Previously known to avoid close combat in favour of psychic trickery and the use of ranged weaponry, their development into a legion of Chaos Sorcerers and the effect of the Rubric of Ahriman only increased reliance on this approach. Those marines affected by the Rubric are used to anchor an attack’s firepower, while the sorcerers deploy their psychic powers, the whole event orchestrated in accordance with a previously constructed plan of deceit or guile. While showing no overt favouring of vehicles or heavy armour, the loyalist Thousand Sons did appear to deploy significant Legio Cybernetica assets in battle, although, in a fore-echo of what would come to pass with the use of Rubric Marines, they psychically controlled the robots to act as a mobile bulwark, rather than letting them operate as normal. The transition into a Chaos Legion did little to change the Thousand Sons’ lack of interest in vehicular or heavy armour support; the discipline of machinery is one that most Sorcerers apparently care little for…although now and again one will take enough of an interest to produce something unusual. The existing Legion stock of vehicles and equipment has rarely been remarked upon since the end of the Thousand Sons’ Imperial loyalty (indeed, it is not actually known if the Legion managed to retain anything other than those Legionaries who were transported from Prospero to the Planet of Sorcerers), but it is known that they sometimes scavenge or steal such items during raids. However, as the Thousand Sons show markedly little interest in properly maintaining their traditional armoury, these repurposed goods never last long and certainly do not appear in large numbers.

While they avoided dissolution as a legion for some time, the Thousand Sons now only seem to operate abroad as small warbands. These warbands are said to seek out conglomerations of psykers, or traces of sorcerous techniques using artefacts known as Seer Stones. Whilst the plans of the Thousand Sons are never easy to discern, being chosen as Tzeentch’s favoured agents results in the actions of their warbands being varied and often curious; by raiding a particular planet, location or killing even a single, specific individual, the manipulations of Tzeentch are furthered. The most well-known of these warbands is the Prodigal Sons warband led by Ahriman.

The Rubric of Ahriman

With the embrace of Chaos, comes mutation. Once the Thousand Sons had retreated back to the Planet of Sorcerers within the Eye of Terror members of the legion began to suffer the flesh-change; horrendous physical mutations, their bodies and minds twisted in ways only Chaos can achieve. Although some dedicated Tzeentch worshippers saw these changes as a sign of their god’s favour, those of higher understanding knew better, and decided that the Thousand Sons’ search for enlightenment and knowledge could not end in the dreaded transformations they would inevitably suffer. Ahriman, once Chief Librarian of the Legion, and second only to Magnus in power, united a conclave of his most trusted sorcerers, and together they cast a spell, known as the Rubric of Ahriman, of tremendous magnitude that would save the legion from the fate of mutation. The results were not what Ahriman expected…but he was satisfied with them none the less. The Thousand Sons were now safe from the taint of chaos, but at a terrible price. Those untouched by the flesh change had their psychic powers greatly strengthened, but those who had already mutated had their physical bodies reduced to dust and their animate spirits damned to live inside their armour forever. Most of the legion were therfore changed into Rubric Marines; little more than mindless automatons. When Magnus heard about the terrible failure, he banished Ahriman and his group from the Planet of the Sorcerers, and now they wander through the Eye of Terror and beyond, still pursuing magical knowledge and seeking arcane artifacts. Ahriman’s current goal is to enter the Black Library of the Eldar, and rumour has it that if he succeeds in his quest, his power will grow beyond imagination.

Vendetta with the Space Wolves

After the destruction of Prospero at their hands, the Thousand Sons have been long time arch-enemies with the Space Wolves chapter. They have tried several times to uproot and destroy the Wolves, ranging from a full-scale invasion of the Space Wolves’ homeworld of Fenris to plots such as those spearheaded by the sorcerer Madox.

This vendetta would have an irrevocable effect upon the legion. The Thousand Sons had largely retained their legion organisation and structure after the Heresy, even raising and maintaining a large body of mortal troops they referred to as Spireguard in an echo of the Crusade-era Imperial Army regiments of Prospero. However, the last known act of the Thousand Sons as a legion was the Battle of the Fang, in which Magnus committed almost all of their remaining assets. At that time, there were approximately 700 members of the Thousand Sons left (not including the coven of Ahriman). Their defeat resulted in the loss of several of the remaining senior legion members, several squads of Rubric Marines, much of their fleet and nearly all of their mortal units.

However at the end of the 40k Millenia the skies of Fenris are aflame, the awful truth revealed. The Thousand Sons, again became architects of the Space Wolves’ darkest hour, launching an arcane invasion across realms sacred to the Sons of Russ. The bringer of this system-spanning doom is Magnus the Red, who visited devastation upon the Fenris system, claiming enough souls to enact a warp ritual of immense power that brought the Planet of the Sorcerors out of the Eye of Terror and set it in the Prospero system, alongside the Thousand Sons original homeworld.

Learn More of the Thousand Sons



  • BT

    To me, the holes that appeared in the legions after the Hersey were always pretty glaring. I always wondered why a army like the Sons didn’t use Techmarines or be more invested in demonengins. Or why every Psyker /has/ to be a former Librarian when the fluff always talks about how normal officers or even troops can have trace psyker powers.

    I have always felt that as psyker heavy as the Sons were, that you should be able to buy normal characters for your list and either be forced to add on a level of Psyker or at least have the option. Sure, it makes them more expensive, but it is also fitting fluff-wise. A former Apothecary might become a Biomancer. A Chaplain that does Telepathy or a Tech Priest that is the driving force to create Rubric automaton or vehicles based off of the Machine Spirit with Demonic Possession. They really should have been the Chaos version of the Grey Knights.

    The current fluff is pretty horrible if you think about it… they are really a dead legion. They have no way to ever replace their losses. They can’t create new marines and they keep throwing away the Rubric Marines and low level sorcs left and right. Really painted themselves into a corner… who knew Tzeentch was so dumb.

    • euansmith

      Apparently it is all going just as planned.

      But, yeah, psychic-everything would be fun for the 1,000 sons; everyone of Sergeant rank and above having at least one psychic power.

    • Anasa

      I recall some lore aspects describing the Thousand Sons conducting a ritual where the fallen rubrics’ souls are snatched back from the warp and placed into new, intact suits of power armor. This ritual may also be applied on other souls, explaining the occasional appearance of rubric marines in other traitor legions, such as the Black Legion.

    • Fergie0044

      “they are really a dead legion. They have no way to ever replace their losses”

      Welcome to the GRIM DARK!
      But seriously, even if this is true (GW could hand wave it away at any moment) who cares? They are merely pawns, be used as such by both their big red master and tzeentch alike. TS have always been a low number legion, twice in their history being reduced to literally their name. And was before the battle of the fang which saw them take large losses.
      GW will never commit to a number in the current timeline, with their always being exactly enough that the story requires, but the lives the traitor legions currently lives isn’t sustainable at all. They are all dying legions.
      If time didn’t work differently in the eye, the last two chaos marines would have died long ago, fighting over the last crumb of food, in a derelict space ship, clubbing each other over the head with empty bolters.

    • Apocryphus

      “who knew Tzerntch was so dumb.”

      Tzeentch’s plans are unknowable by simple mortals, there are twists and turns and interlocking events that are impossible to document, much less comprehend. For all you know, this was all a ploy to make you believe he is not as clever as he is portrayed so that you lower your guard. We are all just pawns in the great changers schemes and to assume otherwise is to be blind to your fate.

    • Aura1

      The Sons replace their losses the same way the other traitor Legions do – capturing suitable individuals in their raids and forcing them to become fresh heretic Astartes. I guess the Sons will favour psykers but the geneseed of Magnus apparently has some capacity to turn on the psyker mutations in those not-‘born’ to them.

      There’s plenty of stories of CSM Legions capturing slaves and replenishing their numbers and since the TS were always rather comfortable with being the smallest Legion, can’t imagine they’re desperate to have untold Star filling numbers.

      Besides, worst comes to worst, they can always put Fabius Bile on speed dial and order up a batch of terata…

      • BT

        With what gene seed? You lose 99% of your gene seed when it all turns to ash inside the Rubric marines along with everything else. The only seed left are in the Sorcs, and that is nowhere near enough to keep up numbers… plus if you make more Rubric your going to lose it. It is a no win situation.

  • Grumpy Scot

    Thousand Sons can make new rubricae, in some sources. Also, I think they drew out the souls of the dead from Prospero to make even more. I think Tzeentch would help them out if required.