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