During the [[Dark Age of Technology]], the two empires of Terra and Mars co-existed, to the mutual benefit of both. At the height of its splendour during the Golden Age, and even later in the anarchic [[Age of Strife]], Mars dispatched hundreds of colony fleets into the void. Many perished in the terrible [[Warp Storms]] that engulfed the galaxy at that time, but others survived. Those that did founded new worlds in the name of the Machine God, building on them a likeness of the great factories and temples of their distant home world.

Because of lack of maintenance during this time, Mars' atmospheric radiation shields soon disintegrated, allowing deadly solar radiation to destroy the fragile ecosystem and wiping out sparse vegetation which had taken millennia to cultivate. Mars returned to being the red wasteland of the past. Plagues caused by high radiation levels slew most of the population. Many of the survivors devolved into [[mutant]]s or gibbering cannibals. The destruction of the entire planet seemed likely. However, this was not to be, for a new idea began to spread among the people, a religion of survival - the Cult Mechanicus dedicated to the Machine God.