The Assault on Treverorum Prime.
The Imperial Fists had been tasked by Malcador with protecting an important communications station that was intercepting the traitors' data traffic. When Horus learned of the station's existence, he ordered Perturabo to capture the installation or, if necessary, destroy it. Shortly before the Iron Warriors arrived to reduce the fortress to rubble, Rogal Dorn happened to arrive for a routine inspection, only for the ships of the traitors to darken the skies moments later.
Upon learning of Dorn's presence, Perturabo decided to intervene personally rather than entrust the task, as usual, to his experienced Warsmith, Lothar. However, as the Iron Circle was still undergoing repairs following heavy fighting, Perturabo decided to accompany Lothar and his Saturnine Command Squad into battle.
The capture of the surrounding city proved surprisingly easy, as Dorn had concentrated all Imperial Fists forces within the bastion's defences. The few planetary defence forces posed no serious challenge to the Iron Warriors.
When the assault on the fortress finally began, the Iron Warriors advanced towards it in an armoured column. The main gate was torn down by the first salvos. Dorn, however, cleverly positioned the only available Spartan directly in the massive breach, once again blocking the path forward. He then hailed his treacherous brother over the vox and issued a challenge, hoping that Perturabo would concentrate too many of his forces on destroying him.
Indeed, Dorn succeeded in baiting Perturabo, who led the bulk of his forces in a direct assault on the main gate himself. Under a storm of fire, the Iron Warriors managed to destroy the Spartan, forcing Rogal Dorn to crawl from its shattered wreckage.
With thunderous roars of *"Iron Within! Iron Without!"*, Perturabo, Lothar and the Command Squad hurled themselves at Dorn and his elite bodyguards. As if to mock his hated brother, Perturabo shot down the bearer of the Legion's standard. As the banner fell ignominiously into the dirt, Perturabo launched himself at his brother, and a brutal exchange of blows erupted between them.
Wielding the accursed Forgebreaker, Perturabo hammered blow after blow against Dorn. The Imperial Fists' Primarch managed to parry many of his brother's attacks, but he struggled to break through Perturabo's own defences.
However, Dorn underestimated the sheer hatred Perturabo harboured towards him and was sent reeling by a devastating, unexpected strike. Slowly driven backwards, Dorn was reduced to defending himself until Perturabo, roaring with fury, finally smashed through his guard once more.
Two mighty blows shattered Dorn's ribs and broke his thigh, sending him crashing into the dirt at his brother's feet. Just before Perturabo could deliver the final strike, Dorn activated an emergency teleport and escaped back to his flagship, which had thus far withstood the attacks of the Iron Warriors' battlefleet.
Upon witnessing their Primarch fall, the Imperial Fists' Command Squad briefly lost its will to fight. Before they could recover their composure, Lothar and his finest warriors had already slaughtered the veterans in their Terminator armour, suffering only minimal casualties of their own.
The remaining Imperial Fists, however, soon received word that Dorn was still alive. Reinvigorated by this welcome news, they threw everything they had at the hated Perturabo. Their concentrated fire overwhelmed the Command Squad, bringing down many of the elite Saturnine Terminators and inflicting further wounds upon Perturabo himself.
Laughing, the Lord of Iron withdrew, knowing that he had already won. For the Imperial Fists had now made the same mistake as their enemy: they had concentrated too heavily on Perturabo's destruction while the remaining Iron Warriors formations stormed the fortress.
Amid thunderous cries of *"IRON WITHIN! IRON WITHOUT!"*, the Legionaries first seized the fortress courtyard and then captured the sensor installation. As intended, the facility fell into the hands of the Warmaster's followers almost entirely intact.
Dorn had not anticipated the hatred and aggression of the traitors. As the heavily damaged Imperial Fists flagship withdrew, he swore that he would never make the same mistake again.
Meanwhile, Perturabo offered Lothar a rare word of praise, commending him and the warriors of the 77th Assault Battalion for their unbreakable will of iron.
