War of Rust and Ruin
However they were soon confronted by his Brother Perturabo and a vast host of Iron Warriors and Chaos Titans from the Legio Abhorrax. The confrontation quickly descends into open warfare, as the Daemon Primarchs lead their forces against each other and both sides summon Daemons to aid them. Though the Iron Warriors and Legio Abhorrax inflicted horrible casualties amongst the Death Guard, the longer the fighting raged, the more the Death Guard's contagions and metaliphage poxes spread throughout Perturabo's forces. The tide of the battle then turned, as Iron Warriors began to collapse and both their war engines and the Chaos Titan's of Legio Abhorrax, start to shut down; due to rust and the uncontrollable corruption of their machine spirits. Mortarion then seized the opening this gave his warriors and Perturabo was soon forced to flee, as the Death Guard's contagions had left his forces in tatters. Badly mauled but triumphant, Mortarion and his Death Guard were now finally able to lay claim to the heathen temple they fought so hard for and the ancient secrets that lay at its heart.