Legio Praesagius - Horus Heresy: For seven Terran years the bulk of the Legio Praesagius was to remain on Gantz, both as a sentinel force to protect the growing forge cities and to rebuild and repair their damaged god-machines.The True Messengers were not idle in this time however, for Ultramar yet remained a border realm, ever ready for attack and still expanding its reach.  Though it could not yet muster in full force, it was rare for an Ultramarines task force to leave Ultramar on campaign without at least a maniple of the True Messengers in support, and many worlds of Guilliman's realm were to host demi-Legio forces during times of crisis.The worlds of Magniat and Orizus were both brought into Ultramar at the point of Legio Praesagius cannon, and the Hrud migrations which threatened Prandium in 005.M31 were only repulsed by the efforts of their Titans and veteran crews. By mid-006.M31, the Legio Praesagius was once again at full strength, now fully entrenched as wardens of the growing and prosperous forges of Gantz and renowned throughout Ultramar for their valour.At the dawn of the Horus Heresy, the might of Praesagius was called to war to help counter the growing Ork threat at Ghaslakh. The True Messengers assembled for their first full-Legio deployment in solar decades.Mustering on Calth in a grand procession as they embarked upon their landing craft, they were betrayed by the Word Bearers Space Marines. Caught unawares, the majority of the Legio Praesagius was ruthlessly destroyed in the opening salvo of treachery, as their dropships were blasted from near-orbit and their parade-ready Titans were ambushed by their erstwhile allies amongst the treacherous Legio Suturvora.It is a testament to the courage and discipline of the Legio Praesagius that, faced with such shocking catastrophe and brutal losses, they succumbed neither to panic nor disarray in the face of the onslaught. Those of the True Messengers who remained active after the initial storm of firepower quickly recovered and mounted vital counter-attacks in support of the Ultramarines and Imperial Army regiments on Calth.Though they were diminished, the Legio fought bravely to the last in the hell-haunted ruins of Ithraca City as Calth's star died, ravaging the planet below. Every Titan of the Legio Praesagius on Calth sacrificed themselves in battle against the Legio Suturvora, allowing other loyal survivors to seek shelter and live to fight another day.When news reached Gantz of the betrayal at Calth, the remainder of the True Messengers swore a Crusade of Iron against the Traitors rampant within the Five Hundred Worlds of Ultramar.The Legio Praesagius, alongside their allies of the Legio Oberon and the Ordo Sinister, dispatched their maniples across the worlds assailed by the enemy, to hunt and to punish the Traitor Legios in dozens of brutal conflicts, and though they were few, every Titan tallied many times their own number in kills before being laid low. In the wake of this crusade, the remnants of the Legio Praesagius would not be content to limp back to Gantz, but once again began the effort of re-marshalling their strength, to join the Ultramarines on their long and difficult road to Terra.