|Map||Basic Data||Planetary Image|
|Affiliation:||Imperium (Adeptus Mechanicus, formerly Black Templars)|
Close to three thousand years prior to Stygia XII's official settlement date, Marshal Gervhart of the Black Templars founded the chapter keep of Montgisard on the planet. It served the Marshal as a base during his execution of the Athelor Crusade and following a millennium of faithful service, it was abandoned by the Black Templars. When Stygia XII was officially settled by the Imperium, the keep's remains were called Stormhelm by the settlers, who considered it a haunted xenos structure and avoided it.
In 832.M41, Montgisard came into importance once more, as it became the base of operations for a Chaos Cult on Stygia XII. They began conducting a ritual to open a gate to the warp, which brought them to the attention of Inquisitor Abraham Vinculus of the Ordo Hereticus. He despatched Interrogator Edwin Savaul to besiege the keep, supported by forces from the Adepta Sororitas and Inquisitorial Stormtroopers, with orders to stop the ritual - if they failed, an exterminatus would be launched on the planet.
They attacked the keep's doors for a week without making progress, the end of each day bringing the ritual closer to completion. Unexpected aid came for them in the form of Castellan Marius Reinhart of the Black Templars' Sword Brethren, who landed on the planet and met with the Interrogator. Reinhart came under orders from High Marshal Ludoldus to reclaim Montgisard, but after hearing of the ritual both sides agreed to work together to destroy the keep.
Using a secret tunnel the Black Templars, Savaul and a group of Battle Sisters entered the keep, while the Stormtroopers launched a diversionary attack. They fought their way through the traitor PDF that made up the majority of the cult and reached the chapel, where the heretic priests were close to opening the warp gate. Unable to attack the priests because of a physic shield, Reinhart entered the shield and detonated a cluster of grenades in his arms as the rest of the group held the surging cult back. The resulting explosion succeeded in stopping the ritual, though only Savaul and two Black Templars survived the ordeal.
Later, after receiving a message for aid from Inquisitor Vinculus, High Marshal Ludoldus brought his forces to Stygia XII. There the Black Templars launched a crusade and destroyed the remaining forces of the cult.[1b]
Stygia XII is a landscape of icy rock and jagged peaks, covered above by a sea of churning storm clouds. The electromagnetic storms affect the machine-spirit of even the most basic devices.
- Capitalis Acheron - City. Primary Administratum centre.
- Montgisard - Black Templars chapter keep. Referred to by the natives as "Stormhelm".