Alternate Heresy

The Horus Heresy is one of the biggest events in the Warhammer 40,000 story. Naturally, people like dreaming up alternate scenarios. Page still being expanded.

In-Universe Alternate Heresy

In Lorgar's visions with the daemon Ingethel the Ascended he gets shown alternate futures in which he stabs Sanguinius and then gets executed by Horus "for his sins", and another one in which he gets taken out by Curze and Russ working together "for defying the Anathema." He also gets instructed by Kairos Fateweaver to avoid at any costs a duel to the death with Corax lest he get his shit pushed in. These are explained as "possible futures" which did not come to pass; in each case it would seem that Lorgar is still the First Heretic (at least in the versions shown to Lorgar himself), but the arrangement of loyal primarchs is different. Notably, in the actual events that ended up playing out, someone who is not Chaos switched the Khan and Fulgrim's fates.

There's also the consideration of the short story "The Board is Set", which details a massive game that the Emps and Malcador had been playing, revealing that the Heresy War was, to some extent, a calculated outcome. The problem was that the meddling of those four assholes had meant that His actions were reactionary, but far from the worst outcome given the circumstances. This was also where big E revealed his final gambit, one that would most certainly screw over the Sigilite.

Deviations

Deviations are generally similar to the original canon but with some changes. In the vein of "What If...?" Marvel Comics. A majority replace the arch-traitor with another primarch. It is something close to an obligation to have Khorne fail to take the Blood Angels.

The Dornian Heresy

The Dornian Heresy was the 40K web forum Bolter & Chainsword's first major project to switch the allegiances of the various Primarchs during the Heresy, and explore what would have happened to the Legions under their command if they had fallen or not.

Unlike the following scenarios, which were largely either FF.net/AO3 stories or thought exercises in random threads on /tg/, this was a full project, with accompanying Index Astartes articles, a wiki and quite a bit of fluff, most of which can still be found quite easily.

Essentially, during the incident on Davin, Magnus the Red arrives on time to exorcise Horus' infection instead of relying on Erebus' rituals. While successful at both saving the Warmaster's life and preventing him from becoming corrupted, it did leave him out of commission. Following their temper tantrum, the Chaos Gods decided that the next best choice was Rogal Dorn, who had been going on overdrive with his pet pain glove.

In the end, we get the following betrayals: The Space Wolves fell to Khorne as part of their rabid psyker-hate. The Blood Angels fell to Nurgle in an event almost identical to the canon Death Guard, plus the bit where they practically owed their lives to Nurgle and were now forced to recruit mutants due to how fucked-up their gene-seed is. The White Scars fell to Slaanesh because Khan got drunk off his vanity and ego while sending his loyal sons to die on Chogoris. The Raven Guard fell to Tzeentch, Corax himself being fed haunting visions of the future by Big Bird himself. The Salamanders fell to Malal out of total disillusionment with the Imperium, and Rogal Dorn himself became the arch-traitor, with his Imperial Fists supporting Chaos Undivided (renaming themselves the Black Legion after the failure of the Heresy). The Ultramarines did not fall to Chaos, but instead became Reasonable Marines; they seceded from the Imperium alongside much of the Ultima Segmentum, and now exemplify progress while fighting off the Tau. The Iron Hands seem to have gotten mixed up with the Necrons, while the Fallen Angels won out over the loyalist Dark Angels, with Luther triumphant.

On the Imperial side, the Word Bearers became the Ecclesiarchy (with no Kor Phaeron to twist it all to heresy - he proved incompatible with the gene-implants), the Iron Warriors remained siege masters, the Sons of Horus became the crusading Black Templars (after almost disowning Horus' foolishness which led to his martyrdom in a manner almost identical to their canonical rebranding), the Emperor's Children remained exemplary perfectionists (except for Fabius Bile, but he's dead now... except not), the Thousand Sons became blind psychic warriors (see: Grey Knights), the Death Guard became the core of the Inquisition, the World Eaters became serious instead of angry, the Night Lords remained loyal Scary Marines without going over the edge, and the Alpha Legion were just as sneaky and just as anti-Ultramarine, but still loyal (apparently The Cabal wasn't that convincing in the Dornian Heresy).

How the Space Marines are organized is also flipped, as the legions falling to Chaos occurred because of them being separated by all sorts of circumstances, so Abaddon (who takes over as leader of the Imperium after the Emperor's battle with Dorn) organized the legions into a few giant armies (by Space Marine standards).

It's pretty awesome...except that, as most alternate heresies are wont to, it all amounts to some absurd amounts of marine-wank (almost as if the whole Heresy is about them, huh). Perhaps the most particular is the Reign of Blood, where the Sisters of Battle never existed, because they were wiped out by the Word Bearers when they were still the Brides of the Emperor, and Goge Vandire (who was now the new Chapter Master following Lorgar becoming a martyr post-heresy) wasn't overthrown by some simple preacher, but by a novice marine named Sebastian Thor. To be fair, can you really imagine the Word Bearers not recruiting him? Meanwhile, all of the xenos factions are left to mere footnotes or mentions (just as Games Workshop intended) and the impact this has had on the Imperium at large is left to interpretation.

The Imperial Heresy

In the Imperial Heresy, the God-Emperor of Mankind decided "if you can't beat 'em, join 'em" and sided with the Gods of Chaos.

The Eldar Gambit

In the Eldar Gambit, Eldrad meets the Emprah the day before the final assault on the Vengeful Spirit, offering assistance in exchange for closer Eldar - Human cooperation later.

The basis of the pact is that instead of taking the mortal blow that Horus throws at him on accident, he does it deliberately, and uses the energy of his own death to attack the Chaos Gods directly, specifically Slaanesh. He steals the stomach of Slaanesh and incorporates it into himself, so now all Eldar souls will go directly to him when they die, keeping them safe from the depredations of Chaos.

The thread was mostly speculation on how a united Imperium of Man and Eldar Empire would work together... and it's actually pretty awesome. Ollanius Pius being revered by guardsmen as an Avatar of Khaine(or Khaine revered as his avatar) and killing Horus right after Horus defeated the Emperor (albeit he was weakened from fighting the Emperor he's a motherfucking Primarch jointly possessed by all Four of the Chaos Gods, there is no "albeit" about it), Space Marines with soulstones to keep the forces of Chaos away from loyal marines, a fractured Adeptus Mechanicus (with four factions - Traitor, Loyal, Machine God fanatics and Fundamentalist (doesn't use Eldar tech that is now more freely available)), and more.

The Roboutian Heresy

The true heresy has begun: Papa Smurf takes the place of Horus and fucks over the Imperium. Much shedding of blood, sweat and tears ensues, with generous helpings of manliness on the side. It's pretty awesome.

Inspired by the above mentioned Dornian Heresy, circumstances happen that lead to the Primarchs who turned traitor in canon to stay loyal and the loyalists to turn traitor. For this Heresy's loyalists this ranges from having a small point that causes a major divergent in their lives, like Konrad and Angron, to having completely different lives like Lorgar. The Traitors all at a certain point have a moment that led them towards Chaos, some better done than others, even the fic's writer admits El'Jonhson's could have been done better, but the rest bring much tragedy and sorrow, though a bit less so with Vulkan (his moment of divergence is absolutely horrifying, but it isn't as sad because of how awful Vulkan and the Salamanders are in this timeline). However, even Vulkan and the Salamander's horrors pale in comparison to that of Corvus Corax and the Raven Guard.

Of the traitors, Vulkan was raised- then killed by, a female fire drake, causing him to realize his immortality early on and gain a god-complex. This wish came true when he, hating the 4 chaos gods but believing SO HARD in his own superiority, actually turned himself into the chaos god of greed and pride! I.e., a giant chaos version of Smaug. Rogal Dorn fell to Khorne due to a massive ork fleet almost destroying the Inquit System and destroying the Phalanx, leading to him never using his magic pain glove to temper his anger. Lion El'Jonson spent too long in the warp-tainted wilds of Caliban and became corrupted by Tzeentch. Sanguinius grew up with an even greater fear of mutants and deviation, causing enough doubts and fear that, when Slaanesh came knocking, he gave himself and his legion up willingly. They then turned into full-on horny space-vampires who get off on drinking blood. For being the archtraitor, Rowboat himself had a pretty lazy bog-standard "hometown and parents were destroyed and became more brutal because of it" backstory as well as being manipulated by Be'lakor, meaning he's a once great hero who turned evil through a combination of losing loved ones and Be'lakor playing him like a fiddle. Jaghatai grew up with chaos worshippers and Russ lost his pet wolves, Geri and Freki, while executing the Lost legions. Ferrus became an utter social darwinist and got infected by Nurgle when he tried to blow up a daemon world. Then there's Corvus Corax, who was in the care of the mad scientists of Kiavahr and, seeing his immense scientific potential, proceeded to slice him up, poison him, disembowl him, tear off and reattach his limbs, and countless other horrific tortures in the name of 'science.' It only gets worse, as he himself became a mad scientist, created horrific astartes clones called Spawn Marines, and became an avatar of a previously unknown chaos god of emptiness and the void (Malal? Worse. Much, much worse.)

For the loyalists, Konrad had a loving mother who helped develop his moral compass into less of a Punisher and more like Batman. When Horus first met his father, their meeting was more cordial and he saw that Big E was just a tired, old man who wanted the best for humanity, under all the glitz and glamour. Magnus fought a titanic psychneuein on Prospero, learning to use his muscles instead of his powers when the creature was immune. When Tzeentch offered to save his sons from the Flesh Change, Magnus said no and basically cured it himself. Now much more cautious, he sent Ahriman to help Horus during the crusade, allowing them to heal Horus and thus the Warmaster never fell. Peturabo, as new Preatorian of Terra, performed a far better job than Dorn did in the Horus Heresy, making a stellar defense for Terra and even constructing huge rings of planetary fortresses around the Eye of Terror and Ruinstorm to keep chaos caged up after the Heresy, called the Iron Cages. By killing his Witchlord foster father, Mortarion learned how to get shit done as he took up the role as Big E's executioner, killing/banishing both Jaghatai and Vulkan singlehandedly before his demise in two separate moments of Awesome. Lorgar and Angron had loving parents and used their psychic charisma to lead revolts against their cruel planetary governments, with Angron never getting the Butcher's Nails, and Lorgar slaying Kor Phaeron when he saw the horrors the cults of chaos were capable of. Fulgrim having a few librarians with him meant he never took up the daemon sword of Slaanesh... buuuut the Eldar didn't know that, so Eldrad convinced the Dark Eldar to kidnap him and subjected him to decades of disgustingly extreme torture so Slaanesh couldn't have him, on the pretense of a faulty prophecy. Thanks Eldrad! Finally, Alpharius Omegon had their pragmatic and ruthless ways tempered by Konrad, so they turned out to be one of the single most valuable chapters of astartes the Imperium has. The Alpha Legion also became buddies with the Rogue Traders, which is pretty cool.

Notably, Fabius Bile is still evil, but a little less so here given that here he has a reason for being evil that his main version lacks, and even he is horrified by the sheer awfulness of the corrupted Raven Guard. On the Flip side, Aeonid Thiel is still on the side of good and was still kicking Traitor Marine ass in the Heresy. Just that said Traitor Marines were also wearing his own colors. Thanks to his theoriticals and stratgems he has made against his foes, alongside being an incredibly crafty fella, he has amassed a bunch of fanboys from the Loyalist Alpha Legion. Not bad.

• Can be read here (also contains sidestories and word of god).

• Can also be read here (see threadmarks) for reactions from the primarchs and the Emperor himself.

The Leonine Heresy

What it says on the label: The-Leonine-Heresy

The First is taking his turn at ruining the galaxy. This is one of the more unique Alternate Heresies in that the primarchs are not swapped 1 for 1, but it is a mix of loyalists and traitors on each side. Mix that with an emphasis on grimdarkness and enough slaughter to impress even Khorne, and you get a story as colossal as the Imperial Palace. Inspired by the Roboutian Heresy and the Shape of the Nightmare to Come/Age of Dusk fanfics.

Like with the Roboutian Heresy, differing circumstances have resulted in drastic personality changes for the various primarchs. For the loyalists, Konrad Curze and Lorgar both got a stern talking to from the Emperor, causing them to remain loyal. Their roster includes Leman Russ (aka Odin), Konrad Curze (blind-folded avatar of justice who sacrifices himself fighting the Archtraitor), Ferrus Manus (WHO COULD FORGET HIM?), Mortarion (pissed beyond belief that he has to be a loyalist), Horus Lupercal (doesn't do too well in the Iron Cages), Lorgar Aurelian (the Saint who arrives too late to save the day), Vulkan (Praetorian of Terra), Corvus Corax (first victim of the Heresy who gets his head pulped like Oberyn Martell), and Alpharius and Omegon (who realized a group of xenos probably aren't the most trustworthy).

For the traitors, we have Lion El'Jonson (Archtraitor as a result of the Rangda and a puppetmaster worthy of Tzeentch) , Fulgrim (Landed on Chogoris, depressed beyond belief because he's the chosen of Nurgle with a Blight-crippled legion), Perturabo (Allied with Vashtorr, Master of the Eye of Terror, and Breaker of Fists and Luna Wolves alike), Jaghatai Khan (lands on Chemos, gets teamkilled by Guilliman), Rogal Dorn (hates Perturabo, hates the Emperor for not making him Praetorian, simple as), Sanguinius (the Red Angel, Chosen of Khorne for once, has the Sanguinor for a stand), Angron (kills Corax, only to be team-killed by a berserk Sanguinius shortly after, his sons have renounced him to serve Malal/Unicron/something), Roboute Guilliman (Chosen of Slaanesh, everything he says is a reference, most often toward David Bowie), and Magnus the Red (Still Tzeentch, but utterly insane; his sons are now wild mutants instead of dusty robots).

Can be read here.

Can also be read here, but with more comments and responses from the author.

Warhammer High

Technically an Alternate Heresy, as in there was no Heresy at all and the Emperor decided Malcador's ideas were not stupid after all and made 19 female Primarch children to give the Primarchs some responsibility Post-Great Crusade, something to live for, a chance for family, and because he really wanted Grandkids.

It's a bit.....weird.

Imperium Ascendant

The Most Fuck-Ass Awesome Timeline: The Legion of the Damned are sent back in time by the Throne-Emperor to stop the scattering of the Primarchs by Argel Tal. After they succeed, the Emperor of the past looks upon the future that is the galaxy of 40K and vows to ensure that such a nightmare will not come to pass as the Ascendant Imperium strikes out against the darkness. In short, The Emperor learns where the Canon timeline will lead, and decides to take corrective measures. This leads two major downsides compared to the main timeline in that Ultramar becomes a Chaos empire instead as Guilliman (Marco Augustio) never landed there to unite the 500 worlds, and Malal is actively out and about feuding the with the 11th Primarch. There is also excellent writing about Gene-seed organs both vanilla and Primaris, plus a few neat extra organs that the original Emperor dismissed as too little utility for available time including a legion specific organ for each legion (akin to the Canis Helix for the Space Wolves, and the Grey Knights get the coolest named one called the Ghost Heart).

The original author threw a hissy fit after TTS announced it would no longer continue and handed the project over to another writer. First part here, and the second here.

The original author got depressed by the chaotic corruption of GW and didn't feel like continuing and handed the project over to another writer. First part here, and the second here.

Nobledark Imperium

Probably one of the more divergent Alternate Heresies out there. Like Warhammer High technically an Alternate Heresy despite there not being a heresy at all. Nobledark is as much a retelling of the 40k universe with intentional twists as it is a straight alternate timeline, sort of like Hektor Heresy or Imperium Asunder, though in general all parties receive a buff to reason and common sense, as you would expect from a universe that is nobledark as opposed to grimdark.

Instead of earning the ever-lasting hatred of the Chaos gods by doing {{REDACTED}} that led to the creation of the primarchs (who in this timeline are the Emperor's greatest, though otherwise similar to canon in name and deed), in this timeline the Emperor plotted with Eldrad and agreed to a last alliance of elves and men a team-up between the nascent Imperium and the Eldar to free Isha from Nurgle’s garden to weaken the Chaos Gods in exchange for access to the Webway and anti-Chaos lore.

The Imperium and Eldar expect to go their separate ways after the Raid on Nurgle's Mansion, until Chaos decides to supercharge the War of the Beast in order to show those mortals what happens when you steal fire from the gods. The Chaos Gods don't manage to turn any primarch (though they get really close with Horus), the Emperor having told the primarchs what Chaos what it is and why it is important to not touch it beforehand. Humanity and Eldar are forced into an alliance once again, resulting in an Aesir-Vanir-esque political marriage between the Emperor and Isha. Although things are bad with the biggest green tide the Imperium has ever seen and Luther convincing the majority of Dark Angels to go traitor, they only gets worse when the true mortal catspaws are revealed.

Because that buff to competence and common sense? Chaos gets it too. And in a spectacular display of long-term planning, instead of consuming ALL of the pleasure cult-worshipping eldar in the Eye upon their birth, Slaanesh only consumed MOST of them. So now in addition to daemons, orks, and traitors, you have an entire army of insane, Chaos-worshipping fair folk who just declared holy war on the Imperium and their heretic kin.

And it all kind of spirals out from there.

Can also be found at Nobledark Imperium Drafts, the other main page for the project.

Shattered Imperium

The canon legions fracture into more than two factions. Imperial Fists, Raven Guard, Salamanders, and Blood Angels remain loyal to Emps. Sons of Horus, Word Bearers, Alpha Legion, and White Scars go Chaos. Thousand Sons, Iron Hands, and Emperor's Children go transhumanist. Death Guard, World Eaters, Night Lords, and Iron Warriors go egalitarian. And finally the Ultramarines, Dark Angels, and Space Wolves go independent of everyone.

MidHammer

The setting that tries to find a balance between the grim darkness of the original Warhammer and BrightHammer.

The Vulkanite Heresy

A less-grim, less-dark, but still solidly grimdark timeline. Vulkan can't stomach the purges of the Lost Primarchs and goes renegade. Eventually this makes him easy prey for Lorgar and Tzeentch, and Chaos gets a Heresy War. Featuring a mix of canon loyalists and traitors in the heretic faction, more renegades and semi-traitors (Oh, Hi Malal), and a decompressed timeline of events. Indexes Astartes are viewable on Ao3 and reddit, with some older material about the primarchs also on reddit. That will eventually be superseded by Biographica Primagenesis entries for them, and some Xenos entries, particularly for changes wreaked on the Eldar, will be inbound, but that will all be after the Index Astartes are finished.

The Sanguinary Schism

A fan heresy with Sanguinus as the traitor warmaster. No wiki yet cause the admin is tech illiterate https://www.facebook.com/SanguinarySchism/

There is also another version of the Sanguinary Heresy, here

If the Emperor Watched If the Emperor had a Text-to-Speech Device

Due to mysterious warp nonsense, the canon timeline just after the triumph of Ullanor when all the Primarchs minus Alpharius Omegon (who arrive later) were together receives the TTS videos and other Lexicanum, 40k Wiki, Codex and 1d4chan information in the form of videos and text files. The Emperor and the Primarchs (minus the twins who as stated arrive later and the lost two who were already purged) watch them to great hilarity. The main thread is on Spacebattles in this thread, while side stories and reactions to fanfiction, homebrews and other files like the wiki articles and the alternate heresies are on this thread. The Extras thread got locked by mods and the main thread is locked due to hiatus so things have moved to SufficientVelocity in this thread. The previous thread has been abandoned. A continuation has been made here.

Main story is written by Praetor98 and sidestories of the main thread and all of the extras thread is made by readers.

Messages for Dad

Possibly one of the most popular fanfictions among the fandom, but many are unaware that it is actually a spin off of If the Emperor Watched If the Emperor had a Text-to-Speech Device, confirmed by Corvus Corax during chapter two of the AO3 Version and by Roboute Guilliman an extra chapter of the SpaceBattles version. He himself started as an extra thread in SpaceBattles for users DuskDawnAndFate and Showtime178.

We follow the imperial family reacting to their future offspring

You can read on SpaceBattles version: Link Here

You can read on AO3 version:Link Here

The Cyclopean Heresy

What if Magnus the Red was the Arch-Traitor? The arrangement of Loyalist and Traitor Primarchs are completely different, with Mortarion of the Death Guard becoming Warmaster of the Imperium during the Heresy, replacing Horus who was stripped of that title when he went traitor.

Can be read here.

Everqueen

Isha manages to avoid being captured by Nurgle and being devoured by Slaanesh, and ends up incarnating to Terra during the Unification Wars. Big E finds her and decides to imprison her and make her his servant as she would very useful to his plans. Author has stated that no, the two will not have a romance between them.

Part one can be read here, and part two here.

Renegades

Shortly before the Canon heresy would have begun, the Emperor decides that he wants to be a god. He allies with the Chaos Gods and ropes in several Primarchs into his plan to make the Imperium worship him as a god. This does not go down well with Horus and Magnus, who start seeing dark changes in the Imperium and the way it is run. They create a coalition of legions to oppose the Imperial legions, and the civil war begins.

Renegades deals with the buildup to the civil war, and the civil war itself. It continues to this day. A good read, and a rather interesting one.

Can be read on AO3 here.

The Fulgrimian Heresy

An alternate heresy where it is Fulgrim who is the Arch-Traitor. Arrangement of Loyalist and Traitor Primarchs are different, with more primarchs remaining loyal to the Emperor than joining Fulgrim and the Traitors. It's an excellent read.

Can be read Link here

Alternate Heresy Community Project

This is an alternate heresy with an interesting premise. Instead of the Primarchs landing where they normally do, they land on different planets, which causes them and their legions to have different personalities and areas of specialization. This causes a different heresy. The thread can be found here

The Alpharian Heresy

Another alternate heresy, where the planets the Primarchs land on are switched up. Alpharian of the Primus Legion falls to Chaos and causes a heresy that splits the Imperium. It consists of three reddit posts linking to documents.

• The Alpharian Heresy, the Primarchs
• The Alpharian Heresy, Corruption of the Primarchs
• First Phase of the War

Blood Tears of the Warmaster

What if a paranoid Cabal killed Horus Lupercal on Ullanor before he could become Warmaster? How would the galaxy change?

Heavily diverges from the average "alternate heresy" type storyline. Really starts to show midway through the plot. Possibly one of the best written alternate heresies out there.

Can be found on Fanfiction.net here

SPOILERS:

• Sanguinius becomes upset over the death of Horus and falls to Chaos to get him back. He eventually becomes the focal point for the creation of the 5th Chaos God, of Sorrow. Terra falls into the Warp, Imperium Secundus is created, and teh Emperor fuses with Cegorach to become the God of Hope

The Lorgar Heresy

Following the Great Treachery of Lorgar, the Imperium of Man was left in ruins. The centuries of strife, revolts, and internicene fighting had undone nearly all of the work the emperor had done during the Great Crusade. Hoping to salvage what remained of a crumbling state The Emperor's Remaining loyal sons reorganized the Empire into a Feudal Kingdom.

Now In the 41st Millenium, the Imperium is finally winning its long and brutal war against chaos, but new threats are gathering. The Eldar and the T'au are rapidly expanding, the ancient alliance between Earth and Mars is rapidly fraying, and devouring swarm has appeared from the deepest cosmos.

You can read the stories of this Heresy on AO3: Link Here

The Corvidian Heresy

Less of an “Alternate Heresy” but more of a “what happens if the Heresy was defeated much more easily?”

Series published on reddit in five parts:

Part one: The Corvidian Heresy: Summary.

Part two: The Corvidian Heresy: Legions I-VII

Part three: The Corvidian Heresy: Legions VIII-XIV

Part four: The Corvidian Heresy: Legions XV-XVII

Part five: The Corvidian Heresy: Legions XVIII-XX

An angel's fall [40k Alt-heresy]

Just another heresy of Sanguinius.

Horus disappeared into the warp on the way to Interex, Dorn and Perturabo united in the traitor team, and For some reason there are Skaven fighting alongside the traitors

You can read in SpaceBattles Here

Warhammer 40K: Legiones Astartes

On the eve of Mankind's greatest victory, with near total domination of the stars, the greatest of the Imperium's commanders and most favoured son of the Emperor - Horus Lupercal - Primarch of the Sons of Horus and Warmaster of the Imperium's vast armies, turned against the light of the Emperor. Convinced by the dark whispers of the Chaos Gods, he led a galaxy-wide rebellion against the Imperium, splitting the domain of mankind in twain. For nine brutal years, the loyal servants of the Emperor fought against their traitorous brothers in a war of almost apocalyptic nature.

Eventually, the Traitor Legions managed to make their way to the capital of the Imperium, to the Throneworld itself - Terra - birthplace of Humanity. In the ensuing battle, countless billions gave their lives in defence of the Emperor of Mankind. The servants of the Dark Gods ravaged and burned the planet, leaving it a husk of its former self. In the aftermath of this apocalyptic battle, Horus lay dead, his very soul destroyed by the psychic might of the Emperor, and the traitors' forces were broken and fled. Losses on the Loyalist side were just as grievous, the Primarch of the Blood Angels, Sanguinius, lay dead, and worst of all, the Emperor Himself had been mortally wounded by Horus in the final moments of the battle, forcing him to be interred in the Golden Throne.

To rule in the Emperor's stead, the leaders of the major branches of the Imperium were brought together in a great council, from which they would forevermore dictate the rulership over the Imperium. Their first act was one of monumental importance, and consequence. The Great Crusade was to be renewed whilst the Imperium rebuilt, as the enemies of Mankind could be given no time to rest. The Horus Heresy had kept Mankind from its manifest destiny long enough, and they would not stand idly by. Whilst the this new 'Second Great Crusade' began, an important factor, once a common sight on the battlefield, was missing. The Legiones Astartes had been nearly shattered by the Heresy - half their number had turned traitor - whilst the loyalists took massive casualties.

The Praetorian of Terra, Rogal Dorn, proposed that the Imperium should not only seek to rebuild the Legiones Astartes numbers, but to eventually expand them even further, by creating new Legions. To help guide these future Legions, they would fall back on the wise tenets of the Principia Belicosa, with additional wisdom added to it by Dorn himself. With the death of the strategically brilliant strategist and organiser Roboute Guilliman at the hands of Alpha Legion assassins, Guilliman's proposed treatise, the Codex Astartes was never completed, and therefore, never adopted. Thus, the dissolution of the Space Marine Legions into separate Chapters never occurred. Soon, the old Legions were rebuilt and returned to the field of battle, joined by brothers of a new generation, seeking to prove themselves in a new war against the Emperor's enemies.

Unfortunately, without the Emperor's guidance and leadership for the last ten millennia, the Second Great Crusade has suffered immensely. The High Lords and their appointed commanders remain unable to counter the threats that lurk in the darkest corners of the galaxy. Billions are slaughtered every day - victims of poorly planned assaults and ill-prepared defences on planetary scales. In this time of everlasting war, there is only one stalwart force keeping the flame of humanity burning - the Legiones Astartes.

More information in the WH40K homebrew wiki and in the WH40K Fanon wiki

IMPORTANT NOTE: Do not confuse this AU with Successor Legions.

Bellum Frigidum: Wtha if The Imperium Never Existed?

One of the many Alternate Heresies being hashed out on the ImaginaryWarhammer subreddit. Premise is, the Emperor loses the Unification War and is killed, but not before the Primarchs are spread throughout the galaxy. No Astartes, the Primarchs never figure out how to reverse-engineer themselves. No Imperium, instead multiple mutually opposing human factions.

A world where humanity remains as divided as it was during the Age of Strife. A world where the Xenos who were once mere footnotes now play a critical role in history. A world where only a few Primarchs are known to each other, and their friendships and alliances are as strange as those of those who live within their empires. A world where chaos is on its last legs and entire civilisations exist only to serve the Dark Gods. A world where the greatest galactic conflict is the impending war between Ultramar and the Mechanicum over who will decide the fate of humanity.

If you want to read more or contribute to the further development of this universe, check out the Google Docs.

The Cipher Heresy

The Cipher Heresy is an alternate Heresy where Leman Russ is the Arch Traitor. Yeah. That's... that's about it.

You can Read in AO3 Here

Heresy of Grey

An alternate heresy featuring more ambiguous motivations, more divided loyalties, Primarchs revealing themselves individually for different reasons, people making bad decisions for sensible reasons, and a very different resulting equilibrium between the Imperium and Chaos.

You can read in AO3 here

Warped Origins

The main focus of this AU is this: “What would the Legions and Primarchs be like if they lived different lives on their homeworlds?” Many Primarchs have their personalities and even their names changed—Alpharius is Warmaster and Emperor's favorite much to "second son" Horus's envy, Corvus *Tyrannus* is raised by Kiavahr's tech-guilds and becomes an unrepentantly cruel slaver and tyrant, Perturabo gets to be happy (at least until the Heresy), and so on. This results in the eventual Heresy playing out quite differently. Horus is still the Arch-Traitor, but his rebellion starts out as one motivated by politics and ideology, and it is the mysterious outsider Gawain Morogan (canon Lion El'Jonson...it's a long story) who corrupts the Traitor side to Chaos.

The two Lost Legions get filled in and explained in this AU as well, playing a small role in the plot.

See the Google document here.

Partial Replacements

Partial Replacements are where the story is generally the same up to a point, but some primarchs are different, such as either the lost primarchs being present, or the primarchs being female

Nobledark Imperium

Probably one of the more divergent Alternate Heresies out there. Like Warhammer High technically an Alternate Heresy despite there not being a heresy at all. Nobledark is as much a retelling of the 40k universe with intentional twists as it is a straight alternate timeline, sort of like Hektor Heresy or Imperium Asunder, though in general all parties receive a buff to reason and common sense, as you would expect from a universe that is nobledark as opposed to grimdark.

Instead of earning the ever-lasting hatred of the Chaos gods by doing {{REDACTED}} that led to the creation of the primarchs (who in this timeline are not the Emperor's sons but instead hand-picked by the Emperor out of exceptional humans, though otherwise similar to canon in name and deed), in this timeline the Emperor plotted with Eldrad and agreed to a last alliance of elves and men a team-up between the nascent Imperium and the Eldar to free Isha from Nurgle’s garden to weaken the Chaos Gods in exchange for access to the Webway and anti-Chaos lore.

The Imperium and Eldar expect to go their separate ways after the Raid on Nurgle's Mansion, until Chaos decides to supercharge the War of the Beast in order to show those mortals what happens when you steal fire from the gods. The Chaos Gods don't manage to turn any primarch (though they get really close with Horus), the Emperor having told the primarchs what Chaos what it is and why it is important to not touch it beforehand. Humanity and Eldar are forced into an alliance once again, resulting in an Aesir-Vanir-esque political marriage between the Emperor and Isha. Although things are bad with the biggest green tide the Imperium has ever seen and Luther convincing the majority of Dark Angels to go traitor, they only gets worse when the true mortal catspaws are revealed.

Because that buff to competence and common sense? Chaos gets it too. And in a spectacular display of long-term planning, instead of consuming ALL of the pleasure cult-worshipping eldar in the Eye upon their birth, Slaanesh only consumed MOST of them. So now in addition to daemons, orks, and traitors, you have an entire army of insane, Chaos-worshipping fair folk who just declared holy war on the Imperium and their heretic kin.

And it all kind of spirals out from there.

Can also be found at Nobledark Imperium Drafts, the other main page for the project.

This Won't End Well(Isekai)

A sorta kinda 40k Isekai, with a unique new 2nd Legion. Later chapters are much less Isekai, and more pure Warhammer AU. Found here. Has some actual tabletop rules written by the author, probably mainly as a way of contextualizing the 2nd Legion within 30k.

Primarch GF

What happens when one mixes the fanart of the Primarchs as female, a meme about fictional characters being your girlfriend, r/grimdank, and the (perhaps horny) insanity of 40k fans? A half serious/half shitpost of an alternate universe where the Emperor decided to make the Primarchs female who would then find themselves a boyfriend. And what was simply a meme posted on Reddit in 2023 would blew up into a full blown “what-if” scenarios ranging from ridiculous to fitting into canon grimdarkness. To the point it spawned its own subreddit and discord. Malcador must be pleased...

The Primarch of Liberty

In an alternate timeline of Warhammer 30k, the Emperor of Mankind discovers the Independence Cluster, a group of technologically advanced worlds that have preserved Dark Age of Technology knowledge. Here, He encounters His first found Primarch, Franklin Valorian, known as the Symbol of Liberty.

The charismatic and humorous Valorian, standing 15 feet tall, meets the Emperor with a mix of curiosity and irreverence. Unlike others, Valorian sees the Emperor as a powerful but regular man with a greater purpose, akin to a superhero.

You Can Read on Webnovel Official

Warning:

• It's a good story but when you read it you will notice that the author really doesn't have much knowledge of Warhammer 40k, something you will notice in the first nine chapters; and some comments theorize about AI writing, plus it has too many jokes.
• 173 chapters and on air, this is going to take a long time.

Divided We Stand: An Alternate History of the Two Lost Primarchs Returned

In the proper timeline of the 41st Millennium, the two primarchs of the IInd and XIth legions were erased for unknown reasons. Two brothers cast aside forever and untouched by the future of Horus' betrayal.

Here such an act of censorship was never cast upon the two. Their stories shall be told. And the effects on the future of mankind shall be far reaching.

This codex shall serve but one possibility; the Lost Primarchs now deeply ingrained to the fires of the grim dark future.

You can read on Wattpad here

Complete Replacements

Complete Replacements are where the story is generally the same up to a point (usually the scattering), but the key difference is a completely new roster of Primarchs and their legions.

The Hektor Heresy, AKA the /tg/ Heresy

/tg/ Creates an Alternate Universe of 40K Astartes legions and discusses how the heresy would play out between them. Since then it has spiralled into a near-total overhaul of the 40K universe as a whole. Although there are variations in quality and completion, the project feature original art and write-ups for the new primarchs and their legions, original regiments of the Imperial Army, a new take on the Squat, and other warhammerania. For those interested in the origins of the project: Archived /tg/ threads can be found at http://archive.moe/tg/thread/34414189/ (Initial Legion creation) and http://suptg.thisisnotatrueending.com/archive/34432982/ (Alternate Heresy thread)

Imperium Asunder, AKA the /tg/ Heresy II: Electric Boogaloo

Yet another alternate Heresy with all-new Primarchs, only one where the Emperor is outright killed and Chaos consumes half the Galaxy, while the Loyalists fracture into a number of warring empires on the Eastern Fringe.

Warmasters Triumvirate, AKA the /tg/ Heresy III: Reloaded

A third alternate Heresy with new Primarchs. After the Emperor is incapacitated relatively early on, he leaves three of his sons in charge of the Great Crusade, the Warmasters Triumvirate. When more power is given to the Council of Terra and regular humans, tensions begin to rise. This one has 21 Space Marine legions, pitted against each other in a three way Brotherwar between the Imperial Loyalists, Chaos Traitors and Confederated Seperatists.

Brotherhood of the Lost

The Icarion Insurrection = First AU created by Brotherhood of the Lost, started on Bolter & Chainsword, with the starting question being: "What if the canon legions were replaced by lost legion projects?" A three-way war between the loyalists, insurrectionists, and the smaller suzerainty, lasting for decades. This AU has since been discontinued and the writers split into the following two new AU's; The Five Ruins and The Broken Throne

Sub-forum can be found here.

Wiki can be found here.

The Five Ruins

The newest project from the Brotherhood of the Lost combining old talent with new blood and legions, the Five Ruins project is set in an ever-escalating conflict caused by the disappearance of the Emperor on His way to Ullanor. 18 new legions and Primarchs who are left to pick up the pieces as the galaxy trembles in anticipation of the horrors to come. A compromise situation is reached, a High Regent appointed, but in the process fundamental differences between certain Primarchs or parts of the Imperium develop that are exploited by the forces of Chaos. The Imperium slowly devolves into a husk of its former self as legions fall to Chaos or lead a breakaway Separatist movement, the Galaxy divided and the fate of Humanity uncertain.

Sub-forum can be found here.

Wiki can be found here.

The Broken Throne

Founded after a certain difference of opinion in the Brotherhood of the Lost project led to the demise of the Icarion Insurrection and a bunch of the creators walked out and took their Legions with them. Warmaster Yucahu of the Void Eagles has been assassinated, the Emperor has disappeared amidst chaos at the heart of the Palace, and the new Lord Regent Kozja of the Warbringers must to pick up the pieces whilst faced with an increasingly violent opposition from other Primarchs. Meanwhile, Ixiplatlan of the Eagle Warriors pulls strings from behind the scenes to incite civil war and spread the reach of the Primordial Annhilator.

Once everybody's figured out which side of this Machiavellian mess they're actually on, the Loyalists must launch an attempt to retake Terra and disrupt Ixipatian's ritual. In the aftermath of the climactic battle warp storms ravage the galaxy, and the Imperium fragments into hundreds of factions striving for their survival.

Sub-forum can be found here

Wiki can be found here.

Legions Reborn

New legions and Primarchs to lead them, not dissimiliar to the Hektor Heresy above.

Wiki can be found here.

Warhammer 30k Alternate Heresy, a collaborative story

It is the 30th millennium. Five-thousand years ago, mankind fell into darkness. The Emperor created thirteen sons and thirteen daughters, great warlords to drag mankind out of Old Night. But mighty alien empires contend against him, worst of all the dreadful Rangdan and the Orks of Ullanor; and in the shadows of the galaxy the Chaos Gods plot the ruin of the Emperor's dream…

You can read in: SpaceBattles, Link Here

Or can read in: Fanfiction net, Link Here

Successor Legions

Created by reddit user Jacob king.

Successor Legions is less of an alternate heresy, and more of a "What if the successor chapters we know of were founding legions?". Presenting alongside these new legions their respective primarchs, 30 legions in total.

There is also some background for the Eldar (including new factions of these), Necrons, Slaugh and Rak'gol; and a few original races

More information on the reddit forum

Or if you prefer more specific information about the successor legions.

This project has been on hiatus for some time now.

The Augustus Apostasy

In a twist of fate, the Emperor molded twenty new sons and their respective legions, an act that would change the past, present, and future of the galaxy.

Eight of them are destined to fall into Chaos, and with their fall, new enemies, dangers, and heroes will be forged, but as always, there is only War.

You can read the Spacebattles version

Or you can read the Fanfiction net version

Projects in Spanish

Due to the incorporation of community projects in the Spanish language by the Latin American fandom, the decision was made to create a separate section that compiles the projects in this language.

Deviations

Astartes Heresy

Created by a member of the Latin American fandom.

What would have happened if no Primarch had betrayed the Emperor but half of the marines of each legion had?

Join me in this universe where perhaps without any traitor Primarch the destiny is even darker...

Warning from Female Astartes of a lost legion

It can be read: Here

The Separatist Heresy

The main events of the Horus Heresy play out much as we know them, save for a few minor exceptions. Such as the homeworld and the names of some primarchs, as well as their legions.

The real change comes after the heresy, when the Primarch of the Thirteenth Legion proclaims independence from the Empire of Ultramar, to which some of his brothers show their support, causing a further division in the already fractured Imperium of Man.

Spoiler:adhuman strain... very suspicious

You can read on Fanfiction.net: Link Here

Warhammer 40k: Imperial Schism

Following the demise of the Emperor, the Imperium of Man faces its greatest crisis yet. Horus the Warmaster attempts to maintain control, but the galaxy is torn apart by factions led by the Primarchs. Betrayal, unexpected alliances and a struggle for power will determine the fate of humanity. Will the Imperium fall to fragmentation or rise again stronger than ever?

You can Read Here.

• Note: The author commented that he believes the story deviated from his original idea, so he was starting to work on a rewrite of the story, when said rewrite is ready a link to this story will also be included.

After a long time, you can finally read the new version of the Imperial Schism here.

And now you can also read the English version here.

Partial Replacements

The Untold Tales

In Rangdan's Xenocides, Denato Pertinax of the Second Legion and Briskaya of the Eleventh Legion arrive to help in the battle but it is too late, their brothers from the Fifth and Twelfth Legion have been purged. How does history change? Who will fall and who will overcome adversity?

Created by a member of the Latin American fandom, The Untold Tales presents one of the most interesting scenarios, A female primarch and female marines, impossible love between a primarch and a mortal woman, changes of sides, two new xeno races, The Rakaven (Skaven) and The Sauri (Lizardmen), eldar of chaos, and many more.

This story receives constant updates on YouTube.

You can see here the First part: Background

You can see here the Second part: Prelude

You can see here the Part Three: Heresy

You can see here The Xenos Saga: side stories about some of the secondary xenos races

Kaon: The Emperor's Bastard Son

Throughout his long mortal life, the emperor had numerous biological children (of which he may never have found out)... Until now, since he has met one of them again, the son of a very... Peculiar mother. How will their presence change the galaxy?

Extra heretical chronicle readable on wattpad.

Warhammer 30/40K Chronicles of a Galaxy in Flames

In this alternate Warhammer universe, the balance of power is very different due to subtle changes, but basically, the major factions have lost a lot of power.

Chaos has been sealed, the Great Crusade has failed, the Tyranids have been devoured, and the Eldar have been punished. The Webway Project has been half-finished, the Primarchs were never part of the Imperium, and the gap left by the Chaos Gods has been filled by all manner of Warp entities of various origins.

If one thing hasn't changed, it's that in the confines of the fortieth millennium, there is only war.

You can read it on Wattpad

Or check out its wiki

NOTE: This fanfic contains stories that assume you already have a good understanding of the Warhammer universe.

Translations

By "translations," I mean works of English origin translated into Spanish by some amateur with enough free time to devote to this task.

The Angel's Tears (A.U. of the Horus Heresy)

Spanish version of Blood Tears of the Warmaster by EndOfEmpires.

An alternative heresy, but not in the way many have done before. Horus is dead, and the consequences are grave.

A new Warmaster will be chosen, and all the Emperor's children will tread new paths, though some will repeat the same one. Eight will defy their Father, willingly or not.

The galaxy will burn.

You can to read in Wattpad Here.

Derailments

Derailments (name pending) are so dissimilar from canon as to be barely recognizable, if at all. History gets completely derailed, probably in the early time periods.

Do you need help?

Do you want to create your own alternate heresy but you are not sure how to configure the sides that will fight in the war?

Fortunately for you, a kind contributor to Heresy Online decided to create a "Guide" that will allow you to build the foundation upon which you can build your heresy (Although let's be honest, whatever you get from following this guide has probably already been achieved by someone else, or if not, someone else has achieved something very similar).

If you like, you can check out the original guide at Heresy Online.

Choose the Archtraitor (Roll 4d6)

Number	Primarch
4	Jaghatai Khan
5	Leman Russ
6	Sanguinius
7	roll the dice again
8	Angron
9	Roboute Guilliman
10	Magnus the Red
11	Lorgar
12	Fulgrim
13	Corvus Corax
14	Perturabo
15	roll the dice again
16	Horus
17	Ferrus Manus
18	Konrad Curze
19	roll the dice again
20	Mortarion
21	Rogal Dorn
22	Vulkan
23	Lion El'Jonson
24	Alpharius/Omegon

Loyalists and Traitors (Roll 1d6)

Number	Alignment
1	Traitor
2	Traitor
3	Loyal
4	Loyal
5	Loyal
6	Traitor

• Remember that there can only be 9 traitor primarchs and 9 loyal primarchs; Now that you have your traitor primarchs, you must choose which Chaos God each legion will swear servitude to (The Arch-Traitor Primarch's legion automatically converts to undivided Chaos, without needing to roll the dice).

Choose a Chaos God (Roll 1d6)

Number	Chaos God
1	The Legion has not dedicated itself to any god and belongs to the undivided chaos.
2	This legion has been dedicated to Tzeentch, the changer of things.
3	The Legion has not dedicated itself to any god and belongs to the undivided chaos (or to Malal if that is in your plans).
4	The legion is transformed by bathing in the blood of its enemies and becomes servants of the Blood God, Khorne.
5	The legion has been taken in by Grandfather Nurgle, the Great Lord of Decay.
6	The legion has dedicated itself to the Prince of Pleasure, Slaanesh.

• If not all of the Chaos Gods have a legion, you must dedicate the last Chaos legion to those gods. If there is still more than one, it must be rolled, but with restrictions so that only one or the other is allowed.

• There may only be one of each of the four gods controlling a legion. If you roll the die and you already have a legion dedicated to that god, it automatically becomes Chaos Undivided (for example, you roll for Space Wolves and get Chaos, then you roll again and get Khorne. But you already have the World Eaters as Khorne, so the Space Wolves become Chaos Undivided).

Now that you have the foundation for your alternate heresy, you can unleash your imagination to create any background/story you wish, perhaps one day you can publish it on this page.

A final side note

The most likely places to find Alternate Heresies, besides /tg/, are the usual fanfic sites (fanfiction.net and AO3), and Spacebattles (+ it's spin-off Sufficient Velocity and related NSFW forum Questionable Questing).

Gallery

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  Loyalist Legions of the Roboutian Heresy
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  Traitor Legions of the Roboutian Heresy
• 
  Loyalists of the Fulgrimian Heresy during the Siege of Terra
• 
  Theoretical Daemon Primarch version of Leman Russ.
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