Event · M31
Battle of Prospero aftermath
The aftermath of the Battle of Prospero, early in the Horus Heresy, was the fall of the Thousand Sons’ home world and the Legion’s turn to Chaos. The campaign is recorded as a consequence of the Edict of Nikaea, which restricted sorcery among the Legions, and of Magnus the Red’s psychic warning to the Emperor about Horus. That warning is recorded as having breached the wards protecting the Imperial Webway project. Horus’s partisans presented the breach and Magnus’s open use of sorcery as defiance, and the Emperor’s judgement was carried out by Leman Russ and the Space Wolves. Russ’s Legion attacked Prospero, and its city of Tizca was destroyed. The Thousand Sons, who were already troubled by the flesh-change afflicting their ranks, were overwhelmed, and accounts differ on the details of the fighting. Magnus is recorded as having been struck down and as having called on Tzeentch for aid, and the Space Wolves withdrew from the ruined world. Ahriman’s Rubric belongs to this period. Later tradition holds that it left most of the Legion as dust sealed within animated armour, while a minority of sorcerers survived in the flesh. The Thousand Sons withdrew to the Planet of the Sorcerers in the Eye of Terror, where they allied with Horus and the traitor Legions. On the Orrery timeline the events fall in M31, during the opening phase of the Heresy, alongside the Isstvan campaigns that followed. Prospero itself remains a ruin, and the Space Wolves’ part in its destruction stayed a source of enmity between the two Legions. Magnus, later a Daemon Primarch, and the Rubric Marines led by Ahriman are the main long-term consequences for the Thousand Sons in the 41st Millennium.
See where Battle of Prospero aftermath occurred on the galactic map during the Horus Heresy.