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The world nearly fell to Heresy when it was invaded by the forces of the Nurgle worshiper Atrophus the Foul, overwhelming its defenders. The Imperium tried to retake Castigon Prime, but every battle with Atrophus's forces resulted in unacceptable losses and eventually the order to perform an Exterminatus was given. However, the Virus Bombs used in the operation proved ineffective in killing Atrophus, finally forcing the Imperium to call upon the Grey Knights to end the threat. They descended upon Castigon Prime where they slew Atrophus before cleansing the planet of his forces and any unfortunate Imperium defenders still left alive.