Event · M42

Invasion of the Stygius Sector

The Invasion of the Stygius Sector was a major Chaos offensive into the Stygius Sector of Segmentum Obscurus after the opening of the Great Rift in the wake of the Thirteenth Black Crusade. Tzeentch selected the sector, already troubled by warp storms that hid the light of the Astronomican, as a realm to corrupt for itself while undermining Nurgle’s hold on the Scourge Stars. Cult uprisings and the work of the Changeling prepared the ground; when the true invasion began, daemons and Chaos Space Marines fell upon the sector’s worlds. Daemon Primarch Magnus the Red and his Thousand Sons, together with the Lord of Change M’Kachen and its Great Changehost, took three systems in short order, with only Mordian able to resist at first. When the Astronomican’s light briefly returned, Imperial defenders called for aid and the Stygius Crusade was assembled, but by its arrival seven sub-sectors had already fallen. The crusade broke the siege of Mordian yet suffered severe losses as worlds of the sector mutated and fleets were cast through time by the Warp. Craftworld Ulthwé intervened, not to hold the sector but to warn the Imperial commanders that Magnus foresaw their destruction if they remained; the crusade evacuated under an Aeldari rearguard, and Stygius became the first of the domains Tzeentch claimed for itself in that design. The Iron Hands under Iron Father Kardan Stronos and Iron-Captain Caanok Var refused the retreat, gathered on Mordian with successor Chapters in the Iron Crusade, broke a Night Lords hold under Ahrak Deathshriek, and continued a counter-offensive into neighbouring systems. On Dhobash, Magnus the Red is recorded as commanding the bulk of the Thousand Sons and accompanying daemon hosts in person. Accounts differ on how far Imperial forces later recovered ground beyond Mordian and the Mordian’s neighbouring systems. Space Wolves under Torval Wyrdbane pursued Thousand Sons sorcerers across the theatre after the death of Wolf Lord Vorek Gnarlfist. The invasion remains an open war in the Imperium Nihilus rather than a single decided battle, and it places Magnus’s Tzeentchian host, the Iron Hands’ defence of Mordian, and Ulthwé’s intervention in one contested sector.

See where Invasion of the Stygius Sector occurred on the galactic map in the 41st Millennium.

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