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Horus Heresy

The Horus Heresy is a major fictional civil war in the Warhammer 40,000 setting, set roughly 10,000 years before the main timeline.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 27, 2026|2 min read| Fact-checked

The Horus Heresy is a major fictional civil war in the Warhammer 40,000 setting, set roughly 10,000 years before the main timeline. It centers on Horus Lupercal’s rebellion against the Emperor of Mankind and is widely described as the foundational event of the Imperium of Man.

In-universe history

The Horus Heresy is presented as the cataclysmic betrayal of the Emperor by Horus Lupercal during the end of the Great Crusade. It escalates into a galaxy-wide civil war that reshapes the Imperium and leads to the Emperor’s confinement on the Golden Throne.

Warhammer 40,000 significance

The event is described by official Warhammer sources as the foundation myth of the setting. It explains the rise of the Imperium’s grim, authoritarian future and the enduring division between loyalist and traitor forces.

The Horus Heresy has been adapted into novels, anthologies, audiobooks, board games, a card game, and other media. The phrase can therefore refer either to the in-universe event or to the broader franchise of works built around it.

Key facts

  • The Horus Heresy is a galaxy-spanning civil war within the Warhammer 40,000 universe.
  • Horus Lupercal, the Warmaster, turns against the Emperor of Mankind and leads half the Space Marine Legions in revolt.
  • The conflict is set about 10,000 years before the main Warhammer 40,000 timeline.
  • The war ends with Horus’s death and the Emperor’s mortal wounding.
  • The Horus Heresy is treated as a foundational event in Warhammer 40,000 lore.
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Canadian context

Warhammer 40,000 has a substantial readership and hobby presence in Canada, so the Horus Heresy is a familiar reference point for Canadian tabletop, fiction, and science-fiction fans.

Frequently asked questions

What is the Horus Heresy?
A fictional galaxy-wide civil war in Warhammer 40,000 in which Horus Lupercal rebels against the Emperor of Mankind.
Is the Horus Heresy part of Warhammer 40,000?
Yes. It is one of the central backstory events of the Warhammer 40,000 universe.
Who is Horus Lupercal?
Horus Lupercal is the Warmaster who leads the rebellion against the Emperor during the Heresy.
What happens at the end of the Heresy?
Horus is defeated, and the Emperor is mortally wounded and sustained on the Golden Throne.
Does the name refer to more than one thing?
Yes. It can mean the fictional event itself or the wider series of novels, games, and related works based on it.

References

  1. Wikipedia — https://en.wikipedia.org/wiki/The_Horus_Heresy
    Supports: Basic description of the Horus Heresy as a central Warhammer 40,000 event set about 10,000 years before the main timeline.
  2. Warhammer Community — https://www.warhammer-community.com/en-gb/articles/y7oihj6s/the-horus-heresy-explained-a-short-history-of-the-warmasters-betrayal/
    Supports: Official description of the Heresy as the foundation myth of Warhammer 40,000, including Horus’s betrayal, the siege of Terra, and the Emperor’s wounding.
  3. Lexicanum — https://wh40k.lexicanum.com/wiki/Horus_Heresy_Series
    Supports: Identification of The Horus Heresy as a series of novels, anthologies and audiobooks based on the events of the Heresy.
  4. Wikipedia — https://en.wikipedia.org/wiki/Horus_Heresy
    Supports: Disambiguation showing the term can also refer to board games and a card game.