The Treaty of Mars, known as the Treaty of Olympus Mons to the Adeptus Mechanicus, is the formal name given to the binding agreements that regulate the coexistence of the Imperium of Man and what was then the Mechanicum of Mars since before the start of the Great Crusade in ca. 798.M30. To prevent a wasteful and costly war between the Imperium of Man that was forged on Terra in the wake of the Unification Wars with the techno-empire that had evolved on the Red Planet during the Age of Strife, the Emperor of Mankind proposed a generous compromise that would cement the alliance and collaboration between both entities for the next ten millennia.
The Treaty of Mars granted political autonomy to the Mechanicum of Mars and its Forge Worlds scattered across the galaxy as well as an exception to the Imperial Truth so that the Cult Mechanicus' adherents could continue to practice their faith. The Imperium would provide six Houses of Navigators and Astropaths to the Mechanicum so that it could unite its far-flung empire of lost Forge Worlds and continue its sacred Quest for Knowledge across the stars. In exchange, the Mechanicum would supply the Imperium of Man with the weapons, starships, materiel and technicians required to initiate the Emperor's Great Crusade to reunite all of the human-settled galaxy beneath the banner of the Imperium. To symbolise the alliance created between Terra and Mars that marked the true birth of the new Imperium, the Emperor changed His personal sigil from one of a raptor and lightning bolt -- the Raptor Imperialis -- to the Aquila, a two-headed eagle whose heads represented the twin foundations of the new human interstellar government -- Terra and Mars, Imperium and Mechanicum.
Age of Strife
In times long past, during the Dark Age of Technology, both Terra and Mars maintained separate interstellar empires and collaborated peacefully for the benefit of all Mankind. The onset of the Age of Strife would shatter this amity, as Terra descended into techno-barbarism. On Mars, the situation became even more dire, for the Red Planet's terraformation was still incomplete. Because of the lack of maintenance of the planet's infrastructure during the conflicts that consumed Mars during that period, its atmospheric radiation shields and oxygen generators soon disintegrated, allowing deadly solar ultraviolet radiation to destroy the fragile Martian ecosystem and wiping out the sparse, genetically-engineered vegetation which had taken millennia to cultivate. As other toxins spilled into the environment from the degeration of the world's great macro-industrial complexes, Mars returned to being the red wasteland that had characterised its past. Plagues caused by high radiation levels slew most of the population and many of the survivors devolved into mutants or ghoulish cannibals. Faced with total extinction, a new idea began to spread among the surviving Martian people, a religion that made a religious faith out of the preservation of the technical knowledge required for their continued survival -- the Cult Mechanicus dedicated to the Machine God.
The devotees of this faith, the so-called Tech-priests, sought out ancient technology scattered across the Red Planet that was needed to rebuild temporary radiation shields, atmospheric generators and weapons to defend against the rad-mutants, insane Automata and the dangerous artificial intelligences or "false minds" that had claimed the wastelands as their own. The Cult demanded absolute devotion from its followers, for only by selfless dedication and often personal sacrifices could the needed archeotech be recovered or the planet saved. Under the direction of their Tech-priest leaders, the cultists set about restoring order to their world. They built new subterranean shelters to protect themselves from the radiation storms that now scoured the surface, and constructed new oxygen generators and food processing machines to enable them to live beneath the protective shielding.
Yet there were few shelters even for the Tech-priests and none for unbelievers. Marauders and mutant raiders tried to force their way inside the hurriedly constructed underground warrens. Many of the cultists died defending their shelters and some of these early settlements were destroyed, but the survivors emerged all the stronger and more determined. The Martian people interpreted their survival in the face of tremendous odds as a vindication of their belief in the dogma of the Cult Mechanicus and the protection of the Machine God. Their resolve and devotion to the Cult soon became unshakable as the Age of Strife wore on.
While rival warlords battled over the remnants of the once-great civilisation of Terra, the Tech-priests built Mars anew, and the first temples and settlements dedicated to the Machine God were erected amidst the crimson sands as the Tech-priests cleared away the mutant tribes and insane machines with the tools they recoved from the surface. The Tech-priests scoured the ruins of Mars for surviving advanced technology which they enshrined within the greatest of the Mechanicum's holy places, the Temple of All Knowledge. In time, the towering forge cities of the Mechanicum's Magi rose into the pink sky, as advanced technology and industry returned to Mars.
Now unified under the alliance of Cult Mechanicus theocratic overlords known as the Mechanicum and its ruling parliament, the Priesthood of Mars began to dispatch Explorator fleets blindly into the still-turbulent Warp without the aid of Mars' long-dead thrall-Navigators. The Tech-priests even plundered the surface of war-torn Terra when the opportunity presented itself in hopes of discovering lost technologies as part of the continuing Quest for Knowledge. Facing resistance to their quest on the Terran surface, the Mechanicum soon became bitter enemies with the techno-barbarians which plagued the devastated Earth. In the meantime, each new world discovered across the galaxy by the Mechanicum's Explorators that survived their blind jumps into the currents of the Immaterium was colonised and rebuilt in the image of Mars itself, transformed into a planet-wide manufactory known as a Forge World, where industry was the only true religion.
Emperor of Mankind Comes to Mars
When the Emperor of Mankind finished uniting the feral techno-barbarian tribes of Terra during the Unification Wars fought before ca. 800.M30, He became aware of the existence of the Cult Mechanicus on Mars and the vast, if fractured stellar empire it had colonised. Realising that waging war against Mars and bringing the Cult Mechanicus to heel would be a long and wasteful battle, the Emperor journeyed to Mars in peace with an outstretched hand and made first contact with the people of the Machine Cult at the summit of Olympus Mons, the greatest mountain of the Red Planet.
When the Emperor first emerged from His great voidship surrounded by all the glory and magnificence His psychic abilities could conjure, many of the Mechanicum Tech-priests present believed Him to be the Omnissiah, the mortal incarnation of the Machine God long promised by prophecy. The Emperor eventually earned an audience before the Mechanicum's parliament of Magi led by their Fabricator-General Kelbor-Hal. The arrival of the Emperor set off political turmoil across the Red Planet, for having expunged any trace of mutation in their own gene-stock long before, the Martians were at a loss to explain the glory of the immensely powerful psyker who strode amongst them. Capitalising on this, the Emperor spoke of the legendary times long past in the Age of Technology when Terra and Mars had worked together to form the core of an illustrious interstellar human federation, and told the Martians that He intended to build a new Golden Age for Mankind in the form of His nascent Imperium of Man.
To this end, the Emperor invited the Martians to join Him, proposing to them the terms of a generous alliance backed up by the veiled threat that he would unleash His genetically-enhanced transhuman warriors upon the Red Planet if the Magi refused Him. The Imperial proposal granted political autonomy to the Mechanicum of Mars and its Forge Worlds scattered across the galaxy as well as an exception to the atheistic Imperial Truth so that the Cult Mechanicus' adherents could continue to practice their faith. The Imperium would provide six Houses of Navigators and its Astropaths to the Mechanicum so that it could unite its far-flung empire of lost Forge Worlds and continue its sacred Quest for Knowledge more easily across the galaxy. In exchange, the Mechanicum would supply the Imperium of Man with the weapons, starships, materiel and technicians required to initiate the Emperor's Great Crusade to reunite all of the human-settled galaxy beneath the banner of the Imperium.
The Martians, realising they had much to win by placating the Emperor, and even more to lose if they opposed Him, agreed to the terms of the proposed alliance after some bloody internal strife, an agreement aided by the reality that many amongst the Mechanicum already believed Him to be the Omnissiah. Unable to abandon the religion which defined their existence, the Martians proposed a compromise that the Emperor agreed to with some reluctance: He would be presented to the masses of the Cult Mechanicus as the Omnissiah, the living incarnation of the Machine God, the long-awaited living repository of knowledge and wisdom who incarnated all of the values of the Cult. Despite being a direct contradiction to the Imperial Truth, the Emperor understood that being presented as the avatar of a god was an acceptable evil in order to secure the Cult Mechanicus' assistance, and that attempting to force the Mechanicum to accept the Imperial Truth could wait until the end of the Great Crusade.
At the same time, the Emperor imposed an exigence of His own upon the Mechanicum. Well aware of the sad story of the Men of Iron, the "false minds" who ruled the Martian surface during the early Age of Strife and the inherent danger and vulnerability of certain technologies to the corrupting influence of Chaos, He forbade the Mechanicum to pursue certain types of knowledge, foremost amongst those the development or study of Silica Animus; machines that possessed full self-awareness and were totally independent of human control. The Emperor listed a number of machines and technological concepts that could lead to the combination of technology with the sorcery of Chaos, and ordered those subjects to be considered taboo, and not to be researched by the Tech-priests under pain of execution. Since many such forbidden technologies already existed in various Magi's forge cities or lay hidden beneath the sands of Mars, the Emperor ordered Kelbor-Hal, the ruling Fabricator-General of the Mechanicum, to seal all such devices within a special cache that only He or His trusted representatives could open, known as the Vaults of Moravec. The Mechanicum grudgingly acquiesced to this arrangement, but the restraint on the Tech-priests' Quest for Knowledge, even the pursuit of dangerous knowledge, would create festering resentments within the Cult Mechanicus that would later reemerge during the Horus Heresy over 200 standard years later.
The terms of this political and economic alliance were then formalised in a binding agreement called the Treaty of Mars, known as the Treaty of Olympus Mons to the Tech-priests after the place on the Red Planet where the Emperor had first trod their soil. This treaty would inextricably bind together the Imperium and the Cult Mechanicus for the next ten standard millennia. To symbolise the alliance created between Terra and Mars that marked the true birth of the new Imperium of Man, the Emperor changed his personal sigil from one of a raptor and lightning bolt, the Raptor Imperialis, to the Aquila, a two-headed eagle whose heads represented the twin foundations of the new human interstellar government -- Terra and Mars, Imperium and Mechanicum.
Although this foundational alliance was later threatened during the Horus Heresy and the Schism of Mars, it ultimately endured across the millennia. In the late 41st Millennium, the Mechanicum, now known as the Adeptus Mechanicus, is still an almost autonomous entity within the Imperium, spared most of the attention of the Adeptus Ministorum and Inquisition by the dictates of this ancient treaty which laid the very foundation of the Imperium of Man.
- Imperial Armour - The Horus Heresy - Book One: Betrayal (Forge World Series) by Alan Bligh, pp. 17-19
- Titan Legions Rulebook (1st Edition), pp. 9-11
- Warhammer 40,000: Rulebook (6th Edition), pg. 402
- Warhammer 40,000: Rulebook (4th Edition), pp. 98-110
- White Dwarf 178 (UK), "The Titan Legions" by Rick Priestley
- Mechanicum (Novel) by Graham McNeill, pp. 29, 228, 317