For questions about the Horus Heresy, a time period in the 30th millennium in the the Warhammer 40k universe. Always use in conjunction with the [warhammer-40k] tag.

The Horus Heresy is the prequel era of the Warhammer 40k universe. Set in the 30th millennium it is era of imperial civil war where brother primarchs turn against each other and Horus betrays the Emperor.