Ardium

Ardium is an Imperial Hive World in the Ultramar Sector. The Planet has three subterranean Hive Cities and is famed for its large-scale bio-habitats. Chaos have invanded the planet twice, once during the Ultramar Campaign and once during the Plague Wars by the forces of the fallen Primarch Mortarion.

Ultramar Campaign
Ardium invanded by the Bitter Sons, a warband from the Iron Warriors, they conquered the Hive City Magmaria. Roboute Guilliman lead an assault against the heretic astartes, who had fortified its winding tunnel networks. The Bitter Sons were outnumbered by the 4th and the 6th company of the Ultramarines, despite they were outnumbered they thought on to the last man. Guilliman did reconquered the Hive City Magmaria.

Plague Wars
Ardium got attacked by the forces of the plaguefather Nurgle lead by Mortarion. The Ultramarines aided the planets defence. Roboute Guilliman believed that the Primarch Mortarion had placed a device that does affect mortal men. He did send the Primaris Brother-Captain Felix, the eleventh Captain of the Ultramarines at that time, to destroy that device. As Felix did inspect the device, did it turn out that their Primarch had right and that the device was crafted by Mortarion with Xenos technologie. Felix did destroy the device, the Ultramarines did break the siege by the Death Guard later.