The Missing Primarchs — What Happened to Legions II and XI?
No one knows for certain what happened to the two missing Primarchs. Games Workshop has deliberately kept the fate of the II and XI Legions one of the great unsolved mysteries of Warhammer 40,000, and in-universe all record of them has been expunged from Imperial archives. What we do know comes from scattered hints and deliberate ambiguity designed to fuel speculation.
The Lost Legions are one of the most interesting storytelling decisions in the hobby: a deliberate gap in the lore that Games Workshop has kept open for decades. Looking at what we know, what fans suspect, and why the gap exists says a lot about the setting.
What Do We Actually Know About the Lost Primarchs?
The confirmed facts are remarkably few. The Emperor created twenty Primarchs, not eighteen, and there were twenty Legiones Astartes, numbered I to XX. The II and XI Legions existed and fought, for a time at least, during the Great Crusade. Then something happened to them, and their records were struck from the Imperial archives: their Primarchs’ names, their Legion names and their deeds.
Beyond that, very little is stated outright. The lore doesn’t tell us who ordered the erasure, why it was done, or what became of the Primarchs and their Legionaries. Accounts tend to present the subject as something that simply isn’t spoken of, and the Primarchs who know more are shown keeping their silence.
We also know the timing: whatever happened to the Lost Legions happened before the Horus Heresy. By the time Horus turned, the II and XI Legions were already gone. That is why neither is counted among the nine loyalist or nine traitor Legions. Because it happened during the Great Crusade, many fans assume the order came from the Emperor himself, but that remains an assumption rather than established lore.
What Hints Exist in the Horus Heresy Novels?
The Horus Heresy series, which runs to dozens of novels plus the Siege of Terra sequence, touches on the Lost Primarchs only rarely and never explains them. Characters occasionally allude to the “lost” or “missing” brothers, or to the gaps in the Legion numbering, and the effect is always the same: a sense of a painful secret that the characters know and the reader doesn’t.
Fans have catalogued these passing references over the years, and they are fun to hunt for, but none of them reveals the Primarchs’ names or fates. If you see a claim online that a particular novel “confirms” what happened, treat it with caution: the official position remains that the mystery is unsolved. Our best Warhammer books guide is a good starting point if you want to read the Heresy for yourself.
What Are the Main Fan Theories?
The absence of official information has produced a huge body of fan speculation. None of these theories can be confirmed, but several are widely discussed.
The Rangdan Xenocides Theory: One of the most popular theories connects the Lost Legions to the Rangdan Xenocides, a series of brutal wars against an alien foe during the Great Crusade that cost the Legions involved enormous losses. Some fans suggest one or both Lost Legions were destroyed or catastrophically compromised in these campaigns.
The Genetic Failure Theory: Another popular theory suggests one or both Lost Primarchs, or their gene-seed, were fatally flawed, showing mutation, madness or degeneration. Supporters point to the known flaws in other Legions’ gene-seed, such as the Blood Angels’ Red Thirst and the Space Wolves’ Curse of the Wulfen, as evidence that the Emperor’s work was not as perfect as Imperial propaganda claims.
The Rebellion Theory: Some fans believe one or both Lost Primarchs turned against the Emperor long before Horus did, perhaps refusing the Great Crusade or trying to build an empire of their own. Total erasure would have been both punishment and warning. The obvious objection is that a public example would have made a stronger warning than silence.
The Mercy Theory: A more sympathetic reading suggests the Lost Primarchs were destroyed or removed for tragic rather than punitive reasons, perhaps an affliction that couldn’t be cured or a sacrifice to prevent something worse. In this reading, the erasure spared them from being remembered as failures.
The Cover-Up Theory: Some theories suggest the Lost Primarchs aren’t dead at all but imprisoned, exiled or hidden for reasons too dangerous to reveal, and that the erasure was concealment rather than a clean-up after their deaths.
What Happened to the Lost Legions’ Marines?
The lore doesn’t say. A popular fan theory holds that surviving Legionaries were folded into other Legions, and some fans go further and link this to the Ultramarines’ famously large numbers. That link is speculation, not established lore, and the Ultramarines’ size is usually explained by Ultramar’s recruiting base and Guilliman’s organisation.
If survivors were absorbed, it would add another layer of tragedy: warriors stripped of their Legion, their history and their Primarch through no choice of their own. It also raises questions fans love to debate. Did they keep their original gene-seed? Are there Chapters in the 41st Millennium that unknowingly carry it? None of these questions has been answered officially.
Why Does Games Workshop Keep It a Mystery?
Keeping the Lost Primarchs a mystery is one of the most consistent editorial choices in Warhammer history. Despite decades of fan interest, and the obvious commercial appeal of two new Primarch models, Games Workshop has never filled the gap.
The explanation most often repeated in the community is that the gaps leave room for players’ own stories, and that whatever GW revealed would be less interesting than what fans have imagined over the years. Whatever the original reason, the mystery itself has become more valuable than an answer.
The Lost Legions also do thematic work in the setting. They show that the Imperium’s own history is unreliable: records are altered, truths are suppressed, and the official version of events can’t be trusted. That theme of controlled information runs right through Warhammer 40,000.
Could the Lost Primarchs Ever Return?
The return of Roboute Guilliman, and later Lion El’Jonson, showed that Primarchs can come back into the 41st Millennium. That has naturally led to speculation about the Lost Primarchs too.
It can’t be ruled out. If they were imprisoned rather than killed, a return is at least possible in story terms. But it would mean Games Workshop solving the mystery it has preserved for so long, which seems unlikely.
A middle ground might see their legacy resurface without the Primarchs themselves: a Chapter discovering its true origins, or a fragment of an ancient record coming to light. That would add to the mystery without solving it.
What Do the Other Primarchs Know?
The lore implies that the surviving Primarchs know more than they share, but it gives very little detail about how each of them feels. Much of what circulates online about individual Primarchs’ reactions is fan interpretation rather than anything stated outright.
One detail fans often bring up is Leman Russ’s canonical role as the Emperor’s Executioner, the Primarch sent to deal with those who had to be brought to heel. Some speculate that he was involved in the Lost Primarchs’ fate, but nothing confirms it. Malcador the Sigillite, the Emperor’s closest advisor and the keeper of many of his secrets, is another popular suspect for the hand behind the erasure, again without confirmation.
What Parallels Exist With Real-World History?
The idea of the Lost Legions draws on real historical practice. The most obvious parallel is the Roman damnatio memoriae, the erasure of condemned people from official records: destroying their statues, chiselling their names off monuments and discouraging mention of them. It was applied to several Roman emperors and officials.
There are also parallels with the Soviet practice of removing disgraced figures from photographs and official histories, and with the defacing of monuments to Egyptian pharaohs who fell from favour. The Lost Primarchs tap into a deep human unease about the power of institutions to control history and erase people from collective memory.
Why Does This Mystery Matter So Much to Fans?
The Lost Primarchs occupy a unique space in fan culture because they are a question that may never be answered, and fans have come to accept, even celebrate, that. In a setting that has filled thousands of pages with detail on nearly everything, the silence around the II and XI Legions stands out.
The mystery matters because it trusts the audience. They belong to every fan who has ever imagined what might have been, and that shared ownership is worth more than any official revelation.
Frequently Asked Questions
Were the missing Primarchs loyalists or traitors?
Neither, as far as we know. Both were lost long before Horus turned, so they never chose a side in the Horus Heresy. The lore doesn’t say whether they were disgraced, destroyed or something else, which is why they’re never counted among either the nine loyalist or the nine traitor Legions.
Why are there only 18 Primarchs in the Horus Heresy?
The Emperor created 20 Primarchs, but the II and XI Legions and their Primarchs had already been lost and erased from the records before the Heresy began. That leaves the 18 known Primarchs, nine loyal and nine traitor, who fought in the civil war. The two gaps remain deliberately unexplained.
Do the missing Primarchs have official names?
No. Games Workshop has never revealed the names of the II and XI Primarchs or their Legions, and in-universe their names were struck from Imperial records. Any names you see online are fan creations. Many players invent their own lost Legion backstories for fun, which is part of the mystery’s appeal.
Did the Emperor kill the missing Primarchs?
It isn’t confirmed. The lore only says that something happened to the II and XI Legions before the Heresy and that their records were expunged. Whether the Emperor destroyed them, they died some other way, or they’re still out there is left open, and every theory, including an execution order, is unconfirmed speculation.
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