


The crux of the campaign came on the Agri-world of Calth in the Ultramar Sector, where the Ultramarines successfully broke the Word Bearers' surprise assault after a viciously-fought siege action, though at the cost of terrible casualties and the complete destruction of Calth's atmosphere and once-verdant biosphere.Īs a result of the devastation wrought by the Word Bearers during the Calth Atrocity upon the Veridia System's sun, future generations of Calth's people were required to live deep underground in massive subterranean hive cities to escape their world's radiation-scorched, airless surface. The purpose of the Word Bearers' invasion of the Ultramarines' Realm of Ultramar in the Eastern Fringes of the galaxy was to tie down the XIII th Legion and prevent them from reinforcing their fellow Loyalists as the Traitor Legions marched relentlessly on Terra itself. The campaign was launched by the Word Bearers' Primarch Lorgar Aurelian with the goal of exterminating the XIII th Space Marine Legion outright. The Battle of Calth, also referred to as the Calth Atrocity, was the name given by later Imperial scholars to the treacherous campaign conducted during the early stages of the Horus Heresy in beginning in 007.M31 by the traitorous XVII th Space Marine Legion, the Word Bearers, on behalf of the Warmaster Horus against their hated rivals, the XIII th Space Marine Legion, better known as the Ultramarines. Veridian System's sun poisoned, making surface of Calth uninhabitable Ultramarines bogged down in Underground War with Word Bearers, preventing them from reinforcing Terra
