Founded a few decades before the Horus Heresy, the Legio Perennia's home Forge World of Bronta-Median was close to the seat of Imperial Power in Segmentum Solar. During the Heresy Bronta-Median's ruling Magos Gaius Trasq declared for the loyalist Mechanicum under Kane over Kelbor-Hal's Dark Mechanicum, and the Legio Perennia mobilized for war. The Legion was to be deployed on Terra and defend the world from Horus's onslaught, but while in transit aboard the transport vessel Omnissiax, Alpha Legion infiltrators attempted to seize the ship.
The Alpha Legion, bringing about traitor Princeps, took control of several Perennia Titans within the Omnissiax hanger bay, opening fire. The ship was devastated from within, allowing traitor Legionaires to take command of the vessel. The Omnissiax and its traitor-controlled Titans were then dispatched to Callistra Mundi under the orders of Armillus Dynat.