The Traitor Legions are the nine Space Marine Legions that turned on the Emperor during the Horus Heresy and fell to Chaos. Ten thousand years later they’re still fighting the Long War, and they’re the reason Chaos Space Marines exist at all.
What the Traitor Legions are
Nine of the original twenty Space Marine Legions sided with Horus when he rebelled against the Emperor. Their Primarchs went with them, and so did their gene-sons, which is why the Traitor Legions are counted as a single, defining event in Imperial history rather than a slow drift. Eight of Horus’s brother Primarchs brought their Legions into the rebellion, and adding Horus’s own Sons of Horus gives you nine.
They’re also called Traitor Marines, Chaos Marines, Heretic Astartes, or Traitor Legionnaires. Whatever the label, they’re the most favoured mortal servants of the Chaos Gods.
After Horus was killed at the Battle of Terra, the rebellion collapsed. The surviving Traitor Legions were driven into the Eye of Terror, a warp-saturated region of the galaxy that’s been both their prison and their stronghold ever since.
The Long War and the Eye of Terror
Inside the Eye, the Traitor Legions built their own domain, an Imperium of Chaos where mutation is almost universal and warbands fight each other for gene-seed, slaves, and resources. Ten thousand years of exposure to raw warp energy means few of them have escaped mutation in some form. That infighting is real, but it’s secondary to their shared hatred of the Imperium.
From the Eye they launch raids across the galaxy, ranging from brutal small-scale strikes anywhere in the galaxy to the Black Crusades, apocalyptic campaigns where Abaddon the Despoiler unites Chaos forces to smash the fortress worlds guarding the Eye. The Long War isn’t a metaphor; it’s the name the Traitors themselves use for their ongoing campaign against the Imperium. Their defining motive isn’t rivalry with each other, it’s hatred of the Imperium, and ten thousand years later, avenging the defeat of the Heresy is still their main driving purpose.
How the Legions are organised now
On paper, the Traitor Legions are the only Space Marine Legions still in existence, since the loyalists were broken into Chapters after the Heresy. The old Legion structure only survives on the Chaos side. In practice, most of them have splintered into warbands led by rival Champions.
Sources disagree on which Legions kept their cohesion. The Black Legion, Death Guard, and Word Bearers are usually named as the ones that still function as Legions, though some sources add the Iron Warriors to that list.
Leaders rise by strength and brutality, not formal rank. Squads are often mixed, with little of the old Legion structure left. Ambitious Marines chase the title of Chaos Champion, and equipment ranges from Crusade-pattern power armour to relics from the Heresy.
What a Traitor Legionary is like
A Traitor Legionary is a Chaos Space Marine, standing over seven feet tall with multiple hearts, rapid healing, and a total resistance to pain. They’ve got every advantage of their loyalist kin, plus ten thousand years of war and the favour of the Dark Gods.
Chaos changes them physically too. Flesh merges with armour, helmets twist into flayed skulls, and the corruption often mirrors the daemons of the god they serve. Once a Marine falls, there’s no going back, and they know it. Their former brothers will show them no mercy, and they return the favour.
Why they matter
The Traitor Legions are the original sin of the Imperium. They’re a reminder that the Emperor’s greatest weapons could be turned against him, and that the Imperium’s oldest enemy isn’t some alien race but its own past.
Every Chaos warband, renegade Chapter, and Black Crusade traces back to those nine Legions. Without them, there’s no Long War and no Chaos Space Marines as we know them.
Key facts
- Nine Space Marine Legions turned to Chaos during the Horus Heresy.
- They were driven into the Eye of Terror after Horus died at Terra.
- Most have splintered into warbands led by Chaos Champions.
- The Black Legion, Death Guard, and Word Bearers are often cited as still cohesive.
- They’ve been fighting the Long War against the Imperium for ten thousand years.
- The Black Crusades are their largest-scale offensives, led by Abaddon the Despoiler.
FAQ
How many Traitor Legions are there?
Nine. Horus’s own Sons of Horus plus eight other Legions whose Primarchs joined his rebellion during the Horus Heresy.
Which Traitor Legions still operate as Legions?
The Black Legion, Death Guard, and Word Bearers are commonly cited, with some sources also including the Iron Warriors. Most of the others have broken into warbands.
What’s the difference between a Traitor Legion and a warband?
A Traitor Legion is one of the original nine Legions. A warband is a smaller, often splintered group of Chaos Space Marines, which is what most Traitors fight in today.
Why do they hate the Imperium so much?
They lost the Horus Heresy and were exiled for it. Ten thousand years later, avenging that defeat is still their main driving purpose.