The Eye of Terror is the largest and most infamous warp rift in the galaxy, a swirling purple-green stain across the northern heavens where the Immaterium and reality have fused into a single nightmarish realm. Born in the death-agonies of the ancient Aeldari empire, it has festered for ten thousand years and more, a permanent breach through which the powers of Chaos spill unchecked.
Within the Eye, physics is a suggestion and the laws of time hold no sway. It is the domain of the Traitor Legions, and here the Chaos Space Marines have waited out the millennia, a single day in a Daemon World sometimes passing as a century in the world beyond. Entire fleets of daemon-infested hulks drift among stars that weep and scream, and the hosts of Chaos Daemons walk freely upon worlds shaped wholly by the will of the Dark Gods.
From this hellish redoubt the Archenemy launches its Black Crusades against the Imperium, and for long ages the fortress-world of Cadia stood as the great bulwark against them. The Eye is not merely a place but a wound that will never close, an eternal reminder that damnation waits just beyond the thin veil of the material world, patient and hungering.