The Rielsprit system's third world follows a figure of eight pattern around its two suns, passing between them in a month of endless, searing starlight. The planet has a short winter while it orbits the brown dwarf, a period of harvest and sewing of seed before the intensive summer growing period.

Port Arius has only one major urban centre (Port Arius the name of both the planet and planetside docks), and it is from here that the planet's bounty of foodstuffs is uplifted off world for transportation to the hive worlds of the sub-sector.

Port Arius has high levels of volcanic action, and has suffered numerous fatal eruptions in its history. The worst disaster occurred in 002.M41, when Mount Morgam exploded, destroying the Isle of Lessingham. The following tsunami killed three hundred thousand and wiped out most of the low lying areas of the space port. The levels of ash in the atmosphere caused a worldwide crop failure, which subsequently led to a famine and the death of millions on Irricadia.

While a backwater world, Port Arius is famous for being the birthplace of Inquisitor Nelson Marukami, the Saviour of De Mille's World. His martyrdom against the Schest saved the world from certain enslavement. A small statue is maintained on the farmland he once called home, and members of the Carthaxian Ordo Xenos have a training facility in the mountains of the northern continent named after Marukami.