The Marax system lies within the Prastian straits, and is the region's closest system to Pillarus Prime. Travel between Pillarus Prime and Marax is considered the most straightforward journey through the Prastian straits and the system's prosperity mirrors this link.

Marax comprises seven planets, four dwarf planets, and upwards of eighty satellites. The inhabited planets are Claudus and Eren, two rocky worlds in the primary biosphere. Both are in turmoil due to insurrection amongst their populace.

The Marax system is noteworthy because of the close association between the Imperial Creed and the Cult Mechanicus on its worlds. The unorthodoxy of the local church's practices are viewed dimly by the Carthaxian diocese. Perhaps because of the Mechanicum's power, the church has yet to be excommunicated, and a few outspoken bishops have been censured because of their outbursts on the issue. In certain circles though, the power behind the insurrection against the Mechanicus in the system is thought to come from the Ecclesiarchy.