Zhao-Arkkad

Zhao-Arkkad is a toxic rainforest death-forge in Segmentum Tempestus whose real forges sit underground because the air rusts everything on the surface. It pledged to the Thousand Sons, sent engines to Prospero, then fought a Dark Angels fleet in its own system before the Scouring dragged it back into the Imperium. The Magi still keep entombed Xestobiax Titans they were supposed to scrap.