Titan Legions (Collegia Titanica)

The Collegia Titanica was formed before the Age of the Imperium and was the primary military arm of the Adeptus Mechanicus before the union of Mars and Terra. After the Treaty of Olympus, the mighty war machines of the Collegia Titanica joined the Legio Astartes and Imperial Army in the Great Crusade to conquer much of the Galaxy. As this new Imperium expanded, the Adeptus Mechanicus took many worlds for themselves. These planets were settled and converted into Forge Worlds, and became the bases of new Titan Legions.

During the Horus Heresy, part of the Collegia turned against the Imperium along with almost half of the Adeptus Mechanicus. The Traitor Titan Legions even took part in the Siege of the Imperial Palace. At the defeat of the rebellion, the rebel Titans were driven into the Eye of Terror, along with the rest of those who had sided with Horus.