Changes

During the period immediately following the Heresy, when Dorn led his Legion against the [[Chaos Space Marine|Traitor Legions]], he concentrated especially on Iron Warriors. In the course of his crusade against the Legion, he systematically dismantled the empire they had developed during the Great Crusade.^3b

[[Perturabo]] resolved to retaliate against his brother for undoing his empire and to demonstrate his superiority in siege after the death of [[Horus]] denied him the opportunity to fully destroy the defenses of the [[Imperial Palace]]. To do so, Perturabo constructed the Eternal Fortress on the world of Sebastus IV, a mighty trap designed to ensnare the [[Imperial Fists]] and allow his [[Iron Warriors]] to inflict overwhelming casualties. The Fortress consisted of over 20 square miles of bunkers, towers, minefields, trenches, razor wire, tank traps, redoubts and a system of complex underground tunnels. The defenses of the fortress were shaped as an eight-point star. At the center was a massive bunker intended to serve as a decoy and of no value whatsoever.^3b

Upon discovering the Eternal Fortress, Dorn declared that he would go there and bring Perturabo back to [[Terra]] in an iron cage.^3b His determination to do so had two motivations. First, Dorn of course wanted to continue his crusade against the Traitor Legions and the Iron Warriors in particular. Second, Dorn decided to resolve the [[Imperial_Fists#Codex_Astartes_Crisis|Codex Astartes Crisis]] by accepting the Codex but willed that the entire Imperial Fists Legion would symbolically enter into the [[pain glove]] together and emerge ready and willing to reorganize into Chapters. Assaulting the Iron Warriors' Eternal Fortress provided just such an opportunity.^1b This indicates that Dorn was prepared for his Legion to take heavy casualties and perhaps even invited the prospect.