"Unlike you, whelp, I once walked the same ground as your idol. I breathed the same air as him. And I tell you this, without lie or artifice. He never wanted to become what you have made him! He did not wish to be your god-thing. He abhorred such ideals! The slavery of your crippled, blind Imperium would sicken him, if he had eyes to see it."
Fabius Bile to an anonymous Imperial worshipper
Imperial eagle

The Imperial Aquila, once the symbol of the Imperial Truth

The Imperial Truth is the name given to the atheist, rationalist ideology promulgated by the Emperor of Mankind during the Unification Wars and His Great Crusade to reunite all the worlds of Mankind beneath the umbrella of the newborn Imperium of Man in the late 30th Millennium.

The Imperial Truth was pioneered by the Emperor on Terra even before the Great Crusade began. It was an ideology defined by the core values of reason, science and secular progress. It was intended to replace the older traditions of religion, superstition and faith that had long defined many of the worlds that had fallen into darkness during the Age of Strife after the fall of humanity's first interstellar civilisation.

At its heart the Imperial Truth held that the universe was rational, that knowledge defeated fear and brought freedom from the terrors of Old Night. With this assertion went the denial of the irrational, the superstitious, and faith in powers and principles beyond the knowable.

In the unified Terra and Imperium of Man, there could be no mysteries of the soul, no sorcery, no gods. Those who clung to their ignorance were cast down, their lies silenced in the pyre's roar. The terrors of the past had grown in the shadow of superstition and false belief. If the human future was to survive its rebirth, it could not tolerate the delusions of the past.

That there were other dimensions, alien species and mutants who wielded psychic powers was not denied, only that they were supernatural. That some might call these phenomena "sorcery," or attribute them to gods, were simply the symptoms of incomplete understanding of reality.

Of course, there was a degree to which the Imperium and the Emperor touched upon the irrational and ethereal. The new Imperium had grown from the past, and secular though it might be, much of its power and nature expressed itself in ways that had echoes of the spiritual. In practices such as the taking of Oaths of Moment, the names of the divisions of Imperial power, and the symbols of that power, the Imperium wrapped itself in the clothes of authority woven from dreams that were as old as the gods they denied.


The Emperor Himself declared that Mankind would never be free to progress and advance to its destined position as the pre-eminent intelligent species in the Milky Way Galaxy until "the last stone from the last church was cast down onto the last priest." He purged ancient Terra of all its ancient religions and superstitious beliefs, even going so far as to personally witness the destruction of the final church on Terra's ancient soil after engaging its resident holy man, Uriah Olathaire, in a battle of ideas, wit and dogma.

The Imperial Truth also held that humanity was the species which should rightfully rule the galaxy since its physical form was the most pure and all of the other intelligent alien races, such as the Aeldari, had already tried and failed to maintain galaxy-spanning civilisations. An important element of the Imperial Truth's ideology was the belief that it was now Mankind's turn to find a place in the sun and come to dominance in the Milky Way -- and that humanity was more deserving of such a position than other species.

The Emperor ordered the Imperial Truth to be brought to all the worlds of Mankind, peacefully at first but imposed by war if necessary, because the Emperor believed that unity was the only way for humanity to survive and prosper in the face of a very hostile universe. If this required the unfortunate use of force against those who refused to understand this necessity, then so be it.

While the Imperial Truth upheld the light of reason and science, it did have one proscription: men must never develop artificially intelligent machines. The Emperor remembered that it was the great war fought by Mankind against the thinking machines known as the Men of Iron that had helped to destroy humanity's last united interstellar civilisation at the end of the Dark Age of Technology and He had no desire to see the human race repeat its past mistakes. As such, when the expeditionary fleets of the Great Crusade encountered advanced human civilisations in the dark of space that had developed artificial intelligence, these worlds' populations were simply exterminated outright as potential dangers to the entire body politic of the newborn Imperium.

The Imperial Truth was spread to all of the rediscovered human colony worlds during the Great Crusade, taught to the men of the Imperial Army, spread by the Space Marine Legions, and inculcated amongst the populations of newly discovered and Compliant worlds by scores of Imperial Iterators. The Iterators were a corps of orators and rhetoricians of supreme skill and passion who were attached to every Expeditionary Fleet of the Great Crusade specifically to spread the Imperial Truth.

This creed only further strengthened the Great Crusade, lending the Emperor's symbolic support to all of the scientists, skeptics and thinkers on whom the Emperor's plans for a united, galaxy-spanning human civilisation hinged. The Emperor needed a new renaissance to begin across the nascent Imperium to see His ambitious dreams for the betterment of Mankind fulfilled. The Emperor hoped that a new age of science and technological progress would solidify and consolidate the gains He and His warriors had made in achieving a new place for Mankind in the galaxy, a restoration of humanity's rightful place as the predominant intelligent species in the known universe.

However, the dominance of the Imperial Truth was already under attack solar decades before the Horus Heresy even began. A text known as the Lectitio Divinitatus calling upon all of humanity to recognise the Emperor's divinity as the one, true God of Mankind had been authored by none other than the Primarch Lorgar of the Word Bearers Legion.

Lorgar had been raised on Colchis, a theocratic Feudal World dominated by priests and the worship of the ancient polytheistic gods of what was called the "Old Faith." Lorgar had overturned the Old Faith in pursuit of a new religion called the Covenant of Colchis that saw the Emperor as a god incarnate after Lorgar had suffered from visions throughout his youth of a god-like figure that would eventually stand beside him.

These visions, probably psychic in origin, proved true when the Emperor came to Colchis to collect His lost son. In the interim, Lorgar, alongside his mentor and foster father, the Covenant's high priest Kor Phaeron, had launched a successful six-year-long holy war against the adherents of the Old Faith on Colchis to force them to convert to the worship of the Emperor.

After Lorgar finally met his father, he penned the Lectitio Divinitatus which taught that the Emperor was the only god deserving of worship by Mankind. The text spread rapidly through the expeditionary fleets of the Great Crusade, and received more support amongst the civilians and support personnel of the fleets and Compliant Imperial worlds than with the Imperial Army's officers and the Astartes, who believed more strongly in the Imperial Truth because of their closeness to the Emperor.

Yet, over time many of the people of the Imperium became convinced that the Emperor was truly a divine being and Emperor-worship cults began to spread, gaining more momentum as the onset of the Horus Heresy approached and the influence of the Dark Gods began to wax. This process was accelerated since the Word Bearers would convert every world they made Compliant for the Imperium to their new faith. This policy made that Legion's progress much slower than that of the other Legiones Astartes and ultimately lead to their brutal humiliation as failures in the Great Crusade before the Emperor Himself on the world of Khur, one of the planets where they had successfully spread the faith of the God-Emperor.

This savage rebuke came only after the Emperor ordered the Ultramarines Legion to destroy the great Khurian city of Monarchia where He had been openly worshipped as the God of Mankind. This humiliation played a major part in Lorgar's corruption and fall to Chaos, allowing his First Captain Kor Phaeron and First Chaplain Erebus to convert him to the worship of the Chaos Gods and corrupt his Legion.

Lorgar had always rejected the Imperial Truth and believed whole-heartedly that religious faith was what truly made Mankind strong in the face of adversity. If the Emperor rejected his worship, than he was determined to find the gods of the Colchisian Old Faith that he had once warred against and offer them his devotion. He led a portion of his XVII Legion, the Chapter of the Serrated Sun, on what became known as the Pilgrimage of Lorgar to find these true divine beings.

Lorgar ultimately made contact with them near the world of Cadia close to the Eye of Terror. Lorgar willingly gave his soul to them once he learned that there were truly gods in the universe and that they welcomed the worship of Men. Lorgar became a secret, devoted servant of the Ruinous Powers who feared the imposition of order over the galaxy that the Imperium brought. Lorgar spent the next several solar decades slowly positioning the pieces of a great plot to convert the Space Marine Legions to the service of Chaos and ultimately initiate a great revolt against the Emperor in the name of the Dark Gods.

The Imperial Truth slowly died away as the Horus Heresy progressed and religious faith in the Emperor seemed to offer both spiritual succor and real psychic protection against the growing powers and daemonic threats of the Ruinous Powers. Just as the Word Bearers had once converted whole worlds to the worship of the Emperor, now Lorgar imposed the bloody worship of the Dark Gods upon every world they captured during the Heresy, forcing the inhabitants to memorise his new work of faith, the Chaos-tainted Book of Lorgar.

Once the Horus Heresy ended in the defeat of the Forces of Chaos and the Traitor Legions fled into the Eye of Terror during the Great Scouring, the Imperial Truth's hold on the hearts of Men retreated even more rapidly. Without the Emperor's guiding influence and constant reaffirmation of His desire for the establishment of an Imperial culture based on secular rationalism and materialism, superstition and religion crept back into the hearts of Mankind.

Lorgar had been right about one thing: religion did provide a far surer way to bind humanity together than reason and science. Belief in the Imperial Truth slowly eroded, year by year, world by world, until the Adeptus Ministorum was officially established in the 32nd Millennium and the Imperial Cult was recognised as the state religion of the Imperium by the High Lords of Terra.

The Imperial Cult combined the widespread human beliefs in the God-Emperor who protected humanity from the terrible dangers of the universe into a single, unifying religion that would sweep away the Imperial Truth as false and heretical dogma. Ultimately, the Imperium's state religion lead Mankind towards a decline into ignorance, superstition, intolerance and tyranny, the very things the Emperor had fought so earnestly against. Ironically, by the late 41st Millennium, the Imperial Truth itself would be seen as a heresy punishable by death at the hands of the Ecclesiarchy or the Inquisition.


  • Horus Rising (Novel) by Dan Abnett
  • Galaxy in Flames (Novel) by Ben Counter
  • The First Heretic (Novel) by Aaron Dembski-Bowden
  • The Horus Heresy Book Two - Massacre (Forge World Series) by Alan Blight, pg. 139