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Warhammer 40k Alpha Legion guide

Your primer on the clandestine XXth legion, their origins and why you should collect an Alpha Legion army in Warhammer 40k and Horus Heresy.

Warhammer 40k Alpha Legion sniper in blue and silver power armor, holding a massive rifle

The Warhammer 40k Alpha Legion are one of the most mysterious and secretive groups amongst the Heretic Astartes. Ostensibly a Chaos Space Marine legion like any other, albeit one focused on infiltration and subversion rather than outright warfare, some say that they are still loyal to the Emperor, carefully furthering his plans. Perhaps they are pursuing a completely different agenda, for reasons that aren’t entirely clear even to them.

Whatever the truth may be, the Alpha Legion are a fascinating force to collect and play in both Warhammer 40k and Horus Heresy. If they sound a bit convoluted for you, we have guides to other, more straightforward Warhammer 40k factions, like the voracious Tyranids and belligerent Orks. Otherwise, stick around and we’ll unravel the mysteries of the most elusive of all the Chaos Space Marine legions.

Here’s what you should know about the Alpha Legion in Warhammer 40k and the Horus Heresy:

Warhammer 40k Alpha Legion Chaos Space marines advance on an Imperial Guard position

Alpha Legion lore

Imperial records, never the most reliable sources of information, are particularly conflicted when it comes to Alpha Legion lore. Few sources agree on exactly when the XXth legion was founded, their fighting strength, or even what colour armour they wear!

What is known is that the Emperor of Mankind created the Alpha Legion with covert operations in mind. During the Great Crusade, reports emerged of shadowy groups of Astartes performing assassinations, abductions and other clandestine missions. These Space Marines weren’t part of any known legion and were simply designated “Alpha”.

Warhammer 40k Alpha Legion headhunters in green power armor crouch in ruins

Eventually the Alpha Legion primarch, Alpharius, was discovered, and the Alpha Legion joined their brother legions. This didn’t curb their secretive ways. Their operations became increasingly shadowy and convoluted – though no less effective for it.

Not every Primarch approved of the Alpha Legion’s methods, and some, like Rogal Dorn, were particularly critical of the unforeseen consequences of their covert schemes. Only Horus Lupercal was consistent in his praise for the Alpha Legion – which may have contributed to Alpharius’ decision to side with the Warmaster during the Horus Heresy.

A Horus Heresy Alpha Legion army, a mixed arms force containing air assets, mechanised infantry, and super-heavy tanks

Horus Heresy Alpha Legion

The Horus Heresy Alpha Legion army is really unique, combining powerful legion special rules with some interesting units and wargear. They have a really different playstyle from other Space Marines.

The ‘Lies and Obfuscation’ ability means that Alpha Legion models are always considered to be 2” further away from enemy units than they actually are. Your opponent will frequently find themselves just out of shooting range, or failing charges they should have made. Unlike many legion abilities, this applies to every model in your army, so it’s effective no matter what models you decide to field.

The ‘Rewards of Treachery’ allows the Alpha Legion to take a single special unit from another legion, an incredibly flexible ability. Combined with their own units, particularly the character-murdering Headhunter Kill Team, the Alpha Legion can carefully control the battlefield and outmanoeuvre the enemy at every turn.

A Warhammer 40k Alpha Legion army, with imposing Terminators and a dragonlike heldrake, with dark teal armor

Warhammer 40k Alpha Legion

At the time of writing, there are no unique Warhammer 40k Alpha Legion rules, as the Chaos Space Marine army list only exists in index form. Until the release of the Warhammer 40k 10th edition codex: Chaos Space Marines, slated for Spring 2024, Alpha Legion players have to make do with vanilla Chaos Space Marine rules – or use a fanmade expansion that provides variant Warhammer 40k detachments for each of the legions.

Even with that restriction, there are plenty of ways to reflect the Alpha Legion’s character in your army. They’re known to work from the shadows and make heavy use of regular human operatives, so Cultists and Traitor Guardsmen are perfect additions to the army.

If you enjoy customising and kitbashing your minis, you can use parts from the regular Space Marine range to make Alpha Legion models that are better suited to infiltration than their ornate, spiky and obviously corrupted brethren.

Horus Heresy Alpha Legion Primarch Alpharius model

Alpha Legion Primarch

Uniquely for any of the Space Marine legions, there are two Alpha Legion Primarchs, Alpharius and Omegon. Whether by accident or design, the artificial womb which gestated the XXth Primarch produced twins, absolutely perfect for a legion that prizes misdirection and subtlety.

Alpha Legionaries, whether through a quirk of the gene-seed or deliberate modification, frequently resemble their genefathers. The pale-skinned and bald Primarchs are said to be much closer in size to regular Space Marines than any of their brother Primarchs.

It is impossible for outsiders to know if they are speaking to Alpharius himself, or just a humble Space Marine acting in his stead. Alpha Legion deceptions have even gone so far as to use conditioning and psychosurgery to make an individual think he really is Alpharius, making the fake almost impossible to detect, and have even been used to hide one of the Primarchs’ identities from himself.

Warhammer 40k Alpha Legion Primarch Alpharius, a bald figure holding a spear in scaled blue-green armor

Alpha Legion books

The best Alpha Legion books to learn about the mysterious marines are the Horus Heresy books Legion by Dan Abnett, and Alpharius: Head of the Hydra by Mike Brooks. Legion introduces us to the Alpha Legion’s style of warfare and brings Alpharius into contact with the xenos organisation known as the Cabal, with terrible consequences for the Imperium of Man.

Alpharius is the Primarch’s own account of his early life, in which he claims he was discovered on Earth before any of the other Primarchs. It’s a surprisingly humanising look at Alpharius that shows a Primarch who is very different from what you might expect – but haunted by dangers to come.

Fittingly for the Alpha Legion, some of their best books aren’t technically books about them at all. Deliverance Lost by Gav Thorpe and Praetorian of Dorn by John French feature the Alpha Legion facing off against the Raven Guard and Imperial Fists, respectively.

The Alpha Legion march in force

Seeing the Alpha Legion’s schemes from the perspective of their enemies shows how intricate and dastardly they are. Praetorian of Dorn gets downright convoluted, with contingencies being used that were put in place before the Horus Heresy even started!

Fancy painting an Alpha Legion army? As well as our guide on how to paint Space Marines, we recommend you check up our guide to Contrast paints and alternatives, as they’re a great tool for creating the metallic blue-green frequently used by the Alpha Legion.