Castellax

Castellax was an Iron Warriors fortress-world of slave-forges, drained oceans, and a Witch Wall of caged psykers, ruled by Warsmith Andraaz's Third Grand Company. Waaagh! Biglug and a slave revolt killed the Warsmith in M41 and left the planet to Orks. It is a Medrengard tithe-world, not an Isstvan pin.