The Iron Warriors went on to create citadels throughout the regions they fought in. Small numbers of Iron Warriors were left behind at these outposts, but Perturabo resented being forced to split his army. As time went on they were stereotyped as being the best army for sieges and garrisons, but eventually the Iron Warriors were so worn out that they simply began to enjoy the killing they had to do after the trenches were dug. A particularly vicious campaign was against the [[Hrud]] in the [[Sak'trada Deeps Campaign|Sak'trada Deeps]], a region that Perturabo saw as strategically useless. Nonetheless, he dutifully oversaw the purging of the Hrud despite his legion's heavy casualties, as it was ordered by the [[War Council]]. At the climax of the campaign, as his fleet lay devastated by a Hrud temporal shockwave, Perturabo could only blame the Emperor's vanity for the damage done to his sons on this useless campaign.{{Fn|12b}}

[[Image:angel-500.jpg|thumb|250px|Right|Perturabo and his brother [[Fulgrim]], after their fall to [[Chaos]], battle [[Eldar]] Revenants (not to be confused with 'Revenant Titans').{{Fn|4}}]]

====Rebellion====

====Iydris====

After the [[First Siege of Hydra Cordatus]] Perturabo was approached by [[Fulgrim]], Primarch of the [[Emperor's Children]], who promised the Lord of Iron near unlimited power. The two embarked on a quest to tip the balance of the rebellion in Horus' favour by journeying into the [[Eye of Terror]] and retrieve a weapon known as the '''Angel Exterminatus'''. After a brief boarding action with the ''[[Sisypheum]]'' (which Perturabo allowed to escape due to his disgust of Fulgrim's Legion), the duo arrived in the Eye and quickly landed on the [[Crone World]] of [[Iydris]]. Entering an ancient [[Eldar]] citadel known as the ''Amon ny'shak Kaelis'', the Emperor's Children and Iron Warriors [[Battle of Iydris|had to contend]] with an army of [[Wraithguard]] and [[Wraithlord]]s that had awoken from their slumber. At the height of the vicious battle Fulgrim attempted to betray his brother and slip away, but was pursued by Perturabo. Both soon arrived in a massive spherical chamber, and Fulgrim revealed to his brother that there was no Angel Exterminatus, but he rather was destined to become such a weapon on this world. Furious, Perturabo attempted to attack Fulgrim but was drained of his power when Fulgrim activated the ''Maugetar'' stone that Perturabo had previously received under the guise of a gift. Now with the Iron Warriors Primarchs' power in hand, Fulgrim revealed the purpose of his plan: to achieve ''Apotheosis'', better known as [[Daemon Prince|Daemonhood]].{{Fn|7}}

Later, aboard the ''Iron Blood'' off [[Mars]], Perturabo watches the data coming in regard to the final actions of the Siege of Terra. He violently rages at being denied what should have been his greatest triumph, destroying whatever can be found around him with ''[[Forgebreaker]]''. Now hating both sides equally, Perturabo contemplated killing Horus once he (in his mind by that point) inevitably prevails. Perturabo realized he will need further power to survive in a sea of enemies, and begins to wonder how to evolve himself into something far deadlier.{{Fn|20}}

By the time of Horus' death and the flight of his armies from Terra in the face of [[Roboute Guilliman]]'s relief force, Perturabo was still aboard the ''Iron Blood'' at the edges of the [[Sol System]]. He observed the [[Word Bearers]] constructing a Warp-based device on [[Neptune]]'s moon of [[Laomedeia]] in order to rekindle the power of Chaos in the System and restart the war.{{Fn|26a}} However the Iron Warrior [[Ortag Theokon]] summoned Perturabo to Laomedeia with a signal, leading to him crushing the Word Bearers, mocking their plan, and stripping the moon of all its resources and personnel before withdrawing. Perturabo indicated that he did not intend to run forever, and that he had a greater plan in mind.{{Fn|26b}}

===Post-Heresy===

After fleeing Terra following Horus's death, Perturabo took the opportunity to take vengeance on the Imperial Fists with a trap on [[Sebastus IV]]. The trap was known as the Eternal Fortress, a keep centred within twenty square miles of bunkers, towers, minefields, trenches, tank traps, and redoubts. Upon hearing of this, Rogal Dorn publicly declared that he "would dig Perturabo out of his hole and bring him back to Terra in an iron cage".

Rogal Dorn expected an honourable battle, but this was not to be. Beginning by isolating the four Companies of the Imperial Fists from their orbital support, Perturabo began to carefully divide his enemy and destroy them piecemeal. Some Imperial Fists managed to penetrate the defences and reach the centre of the Eternal Fortress, only to find there was no central keep – simply an open space watched by yet more defenses. The fortress was a decoy of no real value, surrounded by twenty miles of killing ground. By the sixth day of the siege, Imperial Fists Space Marines were fighting individually, without support, using the bodies of their own battle brothers for cover.{{Fn|1a}}

The siege of the Eternal Fortress (later referred to as the "[[Iron Cage]] Incident") lasted for a further three weeks. Relief came in the form of Roboute Guilliman and the Ultramarines, who drove off the Iron Warriors, but the siege left Rogal Dorn a broken man and rendered the Imperial Fists Chapter unable to fight for nineteen years. The gene-seed of over 400 Imperial Fists was sacrificed to the Dark Gods, and Perturabo was elevated to the rank of [[Daemon Prince]] of [[Chaos Undivided]] {{Fn|1a}}.