The dark mechanicum was founded during the Horus heresy when Kelbor-Hal the fabricator general of mars decided to align himself with warmaster Horus Lupercal in direct opposition of the emperor of mankind. In return for his direct support,the warmasters representative Regulus agreed to open the vaults of Moravec.Deep beneath the surface of Mars these vaults contained warp tainted technology and unleashed a viral scrapcode upon the unsuspecting population infecting the systems of those non-afiliated with Horus and changing the very nature of those who were,infusing their augmentations with chaos and creating evil warp enhanced weapon systems to fight those loyal to the Emperor.Some imperialists escaped the damaging effects of the scrapcode thanks to Koriel Zeths noosperic technology but billions died as the warped code shut down safety protocols,turned loyal sevitors against thieir masters and generally wreaked havoc as it spread accros the planet via the myriad methods of data transferal. Once tainted by chaos the fabricator general and his contemparies abandoned all pretense at civility,turning on those unamenable to persuasion in a planetwide civil brawl.Factoriums that had maintained an uneasy truce for centuries walked on oneanother with their mighty engines of war giving in to the bloodlust coursing through their veins and cables. As the dark heretical technology was shared and expanded upon, Ambassador Melgator coined the phrase "dark mechanicum".Being forwarned and forearmed with superior tainted tech,the forces of the dark mechanicum enevitably crushed all opposing factions on the red planet, a job made easier by the fact that the Emperors astartes abandoned the inhabitants of Mars to their fate having made off with as much war materiel as possible.