Highrock was an Imperium Knight World and the Homeworld for the Knights of House Vyridion, who joined the Imperium after their world was discovered by the Primarch Fulgrim during the Great Crusade.
|None, formerly fourteen million
|Unknown, formerly Imperium
|Dead World, former Knight World
The Knights would swear an oath of loyalty to Fulgrim and fought beside the Emperor's Children during the Crusade and would continue to do as the Horus Heresy began, since they believed Fulgrim fought for the Imperium. Truly unaware that Fulgrim had by then fallen to Chaos, House Vyridion fought against numerous loyalist forces and only really began to question Fulgrim's loyalty, when they fought against the Knights of House Riathan. The Knights of House Riathan, implored House Vyridion to see reason and gave them information of what had happened during the Horus Heresy. This left the Knights of Vyridion confused on who truly served the Imperium in the battle with House Riathan and the next time Fulgrim gave them an order to attack the Knight House, they refused. Instead the Knights of Vyridion returned to Highrock, where they left their Knight suits within their fortress the Great Vault; before a few Knights and Sacristans journeyed to Terra to find out the truth of had happened during the Horus Heresy. However, weeks after they left their Homeworld, the enraged Emperor's Children invaded Highrock, because House Vyridion had defied Fulgrim's orders, and left it a lifeless wasteland.