Beneath the gaze of the Cyclonead Statues, Mortarion and his fellow Daemon Primarch Perturabo themselves engage in a spectacular duel that lasts for seven solar hours. It is a battle reminiscent of the incredible conflicts of the Horus Heresy, and Perturabo's sons cause terrible damage to the Death Guard force. Yet the longer the fighting rages, the more the contagions and metaliphage poxes of the Death Guard spread through the Iron Warrior ranks. Ancient Heretics sicken and collapse. Malevolent war engines seize with rust and shudder, sparking, to a halt. Machine Spirits go mad with revulsion and pain, and as the powers of entropy and decay run rampant, the battle swings in Mortarion's favour. With his forces in tatters and many of his precious war engines crippled beyond repair, even bitter Perturabo is finally forced to concede defeat. Falling back to pre-prepared defence lines, he detonates a series of explosive trenches amidst the raging storms and disengages in the ensuing mayhem. Badly mauled but triumphant, Mortarion and his Death Guard lay claim to the heathen temple they fought so hard for, and the ancient secrets that lay at its heart. (Death Guard Codex, 8e)