Kalides Prime - Era Indomitus: Like many other worlds after the formation of the Great Rift, Kalides Prime found itself stranded in the Dark Imperium, cut off from the light of the Astronomican and vulnerable to assault by the forces of Chaos. The planet was invaded by the Death Guard, led by the Lord of Contagion Gurloch.The Death Guard initially bombarded Kalides Prime from orbit using a combination of explosive ordinance and potent contagions. This assault killed almost half of the defending five thousand-strong Cadian 44th Heavy Infantry Regiment of the Astra Militarum and severely damaged the city of Dustrious.The Warp-derived pathogens transformed most of the civilian population of Kallides Prime into Poxwalkers while the survivors, including the Imperial Guardsmen, where afflicted with an unknown disease.Following the bombardment, approximately 300 Death Guard Plague Marines, along with their supporting armoured forces, a legion of Poxwalkers and various daemonic allies invaded Dustrious. Gurloch planned to use the world's astropathic fortress to perform a Chaos ritual intended to unleash a new psychic epidemic across the sector.The Astra Militarum troops of the Cadian 44th Heavy Infantry garrisoned within Dustrious attempted to repel the invading Chaos forces, but were forced to retreat into the city's Temple District after taking heavy casualties. They were aided by the unexpected arrival of the Ultramarines Strike Cruiser Primarch's Sword and the seventy-two Primaris Space Marines aboard commanded by Lieutenant Cassian Talasadian.The Ultramarine strike force quickly secured the orbital defence batteries and landed its entire complement of warriors on the outskirts of the city. The Primaris Marines attempted to push through the city towards the astropathic fortress with the support of the Astra Militarum garrison, but were ambushed by a large force of Plague Marines. After suffering heavy casualties, Talasadian ordered an orbital bombardment from the Primarch's Sword to cover their retreat.However, due to a malefic storm conjured by the Chaos forces, the bombardment proved inaccurate. However, a psychic storm of immense power was soon unleashed on the Death Guard forces which had been summoned by an Asuryani Farseer to save Talasadian's life, for his survival was crucial for the future.After two solar weeks of fierce fighting, only a few hundred men and woman of the Cadian 44th Regiment remained alive along with elements of their armoured division. The Primaris Marines launched a second assault with the support of the remaining Cadians to dislodge the Chaos forces besieging the astropathic fortress. All of the remainingCadian troops were killed but the Ultramarines managed to secure the fortress.During the fighting, Talasadian and Librarian Karitraeus defeated Gurloch, but Talasadian was mortally wounded and Karitraeus was slain. After securing the fortress, the Ultramarines launched another assault to rescue Talasadian and retrieve Karitraeus's body.Within the fortress, the Ultramrines discovered a choir of astropaths along with several members of the fortress garrison who had quarantined themselves against the Death Guard contagions. The choir later transmitted a distress call to the nearest fleet of the Indomitus Crusade.Ultramarines reinforcements led by their Primarch Roboute Guilliman arrived in response to Talasadian's distress-call. For his sacrifice, when Talasadian's wounds proved mortal, he was placed within the cybernetic sarcophagus of a Redemptor Dreadnought.After the defeat of the Death Guard, Kalides Prime was declared Purgatus Extremis and a Dead World by the primarch. The astropathic fortress was bombed into rubble so it could no longer be used and countless servitor-mines were laid throughout the lower atmosphere of the planet to prevent the Death Guard from recovering their ever-resilient warriors.