Of the countless persistent mysteries in Warhammer 40k lore, one forbidden, unanswered question refuses to die: what happened to the two so-called ‘lost legions‘ of Space Marines who disappeared before the Horus Heresy? What did the II and XI Legiones Astartes do that was so heinous, the Emperor had to erase them from Imperial history?
There is a real-world explanation for the mystery, and I’ll get to that, because it’s important. But first, let’s explore some fun, in-universe explanations and fan theories. Here’s the background: the Emperor initially created 20 demigod-like Warhammer 40k primarchs – one deputy to lead each of his Space Marine legions.
But, at some point during the nearly 2,000 years between the primarchs’ creation and the onset of the Horus Heresy civil war, the second and 11th primarchs were utterly obliterated, along with their entire legions, by Imperial edict. All that’s left is tantalizing traces, like the two skulls marked II and XI on the throne of Malcador the Sigillite in the image above.
Their names were deleted from all records, and their thousands of Space Marines vanished from Imperial rosters (though they may have been quietly absorbed into the Ultramarines and Imperial Fists). They became known as the Forgotten and the Purged, and none of their gene-seed survived to form part of the Imperium’s modern Warhammer 40k factions (at least, not officially).
Apart from a few snatched, suggestive comments, even the other 18 primarchs never discuss their abolished brothers during the Horus Heresy books – even those that turned traitor in the Horus Heresy. And we don’t know why.
On the face of it, that may not seem too controversial. The Imperium of Man is a dystopia, after all, and the Emperor was a totalitarian war leader who dictated his own history books and exterminated whole star systems at the stroke of a pen. So what if he purged a couple of his own armies and generals? Stalin did it all the time.
What makes this mystery spicy is that the Emperor of Mankind didn’t make a habit of completely purging his primarchs or their legionaries like this. The primarchs and space marines were extraordinarily costly to manufacture, and he didn’t throw them away on a whim. The overly religious Word Bearers, slaughter-hungry World Eaters, and civilian-torturing Night Lords all disobeyed the Emperor’s edicts flagrantly and often, and were punished for it – but none of them were purged.
So whatever the hell happened with the 2nd and 11th legions must have been either unspeakably awful – or so dangerous to the Emperor’s plans that he couldn’t let the secret get out. So, what was it? We’ll never know for sure – but, based on the evidence in the Horus Heresy novels, we can sketch out a few possibilities.
Option 1: they rebelled against the Emperor
The first, and simplest, possibility is that the second and/or 11th primarchs formally turned traitor against the Imperium – either for their own particular reasons, or due to the machinations of chaos – and were purged for it. It seems somewhat plausible, because, of course, Horus Lupercal did just this when he started his rebellion in the late 31st millennium.
But it took a vast, centuries-long conspiracy of carefully laid plans and warp sorcery to ensure Horus’ uprising wasn’t squashed before it even began – and that was with the Emperor off the game board, busy working on his secret Webway project on Terra.
If one or both of the lost primarchs took up arms against the Imperium during the early Great Crusade, while the Emperor was at the height of his strength and leading his armies personally, they’d have had no chance of survival.
This is conceivable (if foolish on the rebels’ part), but there are a couple of reasons why I don’t buy it. If the second and 11th legions rebelled and were crushed, why ‘forget’ them? Why not make an example of them to show other would-be turncoats the wages of treachery?
A couple of primarchs’ heads on spikes might have dissuaded many of the potential traitor legionaries later on, when Erebus, Lorgar, and the Word Bearers started sowing their seditious ideas through the secret warrior lodges.
More importantly, what little evidence we can glean from Black Library’s Warhammer 40k books suggests the other primarchs (even the ultra-loyalists) remember the lost ones with grief and sadness – not the bitter, righteous hatred you’d expect if they’d simply been rebels that got put down.
For example, in Guy Haley’s 2021 book Dark Imperium, Roboute Guilliman describes the two lost primarchs as having “failed”, rather than lumping them in with the nine traitor primarchs of the Horus Heresy – suggesting their deletion from history was for something more complex or insidious than simple armed rebellion.
Option 2: they knew too much
Another possibility is that one or both of the lost primarchs discovered the truth of the Warp and/or the Emperor’s secret plans – and were wiped out to stop them blabbing to the others.
As discussed in great detail during Dan Abnett’s epic concluding trilogy The End And The Death, the entire Horus Heresy saga is in many ways the story of the Emperor’s doomed attempt to hide the existence of the Warp, and chaos, from all of humanity, including his primarch sons.
Magnus the Red learned more about the Warp than most – but wisely kept his forbidden knowledge strictly controlled within his legion’s arcane traditions. If the second or 11th primarchs came into contact with a powerful Chaos Daemon or other warp entity, and later challenged the Emperor on the magical secrets he’d concealed, it’s easy to imagine Big E deciding that axing one tenth of his elite army was a worthwhile price to pay to hush the whole thing up.
The Emperor’s grand plan was (supposedly) to orchestrate humanity’s ascension into a fully psychic species, able to permanently dominate the galaxy and, eventually, subjugate the ruinous powers for good – but it was fraught with risk.
If any part of the Emperor’s domain – let alone one of his 20 headstrong, demigod sons and their legions of super-soldiers – learned the full truth of the warp and the powerful, god-like entities that inhabited it, it would make a mockery of his atheistic Imperial Truth, and could bring all his schemes crashing down around him. Worse still, if they got wind that the Emperor had himself consorted with those entities to enhance his own powers (which there’s evidence he did), it would add hypocrisy to his list of concealed crimes.
This exact realization was the catalyst which later tipped Horus over the edge into rebellion, while the Emperor was far away on Terra, unable to intercede. If the lost primarchs learned these forbidden truths while the Emperor was still at large in the galaxy, in striking distance, he would have done absolutely anything to prevent the information getting out.
Option 3: they suffered a geneseed crisis
A third possible reason is that the second and/or 11th legions were struck down by catastrophic flaws in their geneseed, causing fatal or corrupting mutations that led the Emperor to dispose of them as failed experiments.
The arcane gene-science used to create the primarchs was not a 100% reliable process, and several primarchs had hidden genetic faults that manifested in various horrible ways among the legions bred from their templates.
The Blood Angels’ flawed genetic code caused marines to be taken over by a ‘Red Thirst’, driving them into an uncontrollable, frenzied hunger for human blood. The Thousand Sons likewise fell victim to the ‘Flesh Change’, causing legionaries’ bodies to degrade and mutate, and eventually turning them into maddened monsters.
If either of the lost legions developed similar defects, early on in the Great Crusade, it could have made them unpredictable and dangerous, potentially leading other legions to suspect they could meet the same fate. If they were purged for this reason, it would explain why the other primarchs’ scattered references to them in the Horus Heresy books seem like grieving a tragic loss, not cursing a betrayal.
James Swallow’s 2012 novel Fear to Tread gives a crumb of evidence to this line of thinking. During the prologue, Blood Angels primarch Sanguinius says he’s keeping his legion’s gene-fault a secret because he “will not be responsible for the erasure of the Blood Angels from Imperial history”, and “will not have a third empty plinth beneath the roof of the Hegemon as my Legion’s only memorial”.
That’s certainly a strong implication that the lost legions’ fate could have been the result of a geneseed-related disaster – and it’s my personal pet theory. But now, let’s get to the bottom of it. Within the lore context of the Horus Heresy series, any of these could conceivably have been the fate of the lost second and 11th legions. In the real world, however, there’s a pretty straightforward bottom line.
The boring, real world answer
The lost legions are a deliberate, unsolvable mystery that GW’s writers wove into their universe to add depth and intrigue. There is no official, in-universe answer to why two of the 20 Space Marine legions are lost, faceless, and mysterious, and there never will be.
Rick Priestley, co-creator of Warhammer 40,000 with the late Bryan Ansell, has explained in past fan interviews that the entire Horus Heresy – including the lost legions – was intended as a semi-mythological, distant past for the setting. We were never meant to know the details – which is why subsequent novels have only ever given us fleeting hints.
Legendary Black Library author Aaron Dembski-Bowden also confirmed in a 2018 Reddit thread that – despite some books’ hints to the contrary – the Space Wolves didn’t exterminate the lost legions, because “that would be an answer”, and “there’s not allowed to be an answer”.
Games Workshop leaves deliberate holes in its grand tapestry of Warhammer 40,000 lore. Some were intended to allow space for fans to create their own ideas – like Priestley’s decision to have at least 1,000 Space Marine chapters, but only give a few of them an ‘official’ GW backstory. But others are simply questions that have no answer, because fictional universes get less exciting, the more we know about them. The disappearance of the II and XI legions is forever one of these.
Don’t despair, though; we 40k fans can and will debate headcanon over these issues until the heat-death of the universe – Wargamer very much included. For more grimdark deep dives, read our articles on what the Tyranids are running from, and the eternal question: is the Emperor really just a massive idiot?
Source: Wargamer
