
The hatred that the loyalist Space Marine Chapters developed towards their former brothers, the traitors who sided with Horus Lupercal during the Horus Heresy, was rooted in betrayal on an incomprehensible scale. Once bound by unbreakable oaths of brotherhood, loyalty, and service to the Emperor, the bonds between the Legions were shattered when Horus turned against the Imperium, leading nearly half of the Space Marine Legions into open rebellion.
For the loyalists, the pain of betrayal was twofold: personal and ideological. On a personal level, they had fought alongside the traitors, shared victories, and spilled blood together for the dream of the Imperium. When the traitors turned to the worship of the Chaos Gods, the loyalists were faced with the stark reality that their brothers had not only abandoned their shared purpose but actively sought to destroy everything they had built together. The sight of once-familiar heraldry twisted into profane icons and hearing the voices of former comrades now spouting blasphemous vows fuelled a deep-seated rage.
Ideologically, the traitors’ rebellion was seen as a rejection of the Emperor's vision for humanity. For the loyalists, this vision was not merely a cause—it was their purpose, sanctified by the Emperor's divinity. The traitors' allegiance to Chaos was viewed as an unforgivable corruption, a betrayal not just of the Emperor but of humanity itself. The loyalists considered their former brothers irredeemable, their souls blackened by the warp and their honour forever tainted.
This hatred festered over the millennia, reinforced by ongoing conflicts with the Chaos Space Marines who emerged from the Horus Heresy as the Imperium's eternal enemies. For the loyalist chapters, the memory of betrayal serves as a grim reminder of the cost of heresy, fuelling their unrelenting resolve to purge the galaxy of Chaos and ensuring that the sins of the past are neither forgotten nor forgiven.
Domine, damnatos in ignem mitte,
Fratres perfidos, in abyssum rite.
Traditores fidei, lux eorum cecidit,
In noctem sempiternam cor eorum abiit