Ryza is one of the greatest forge worlds of the Adeptus Mechanicus, its endless manufactorums shrouded in the actinic glare of plasma reactors and the incense-smoke of ten thousand tech-rites. Above all other things, Ryza is famed for its plasma weapons, forge-patterns so pure and stable that their volatile secrets are guarded more jealously than the lives of the tech-priests who tend them.
Such treasures make Ryza a beacon to every predator in the galaxy. The world has weathered countless sieges, its skies scorched by Ork invasions, its outer districts overrun by the endless swarms of the Tyranids, and its foundries choked by the encroaching corruption of the Warp. Each time the Skitarii legions and battle-servitors of the forge have held, or the ash-choked cities have been reconquered at monstrous cost.
Through it all the sacred data-looms keep turning, and Ryza continues to arm the Imperium's armies with weapons that burn hotter than a sun's heart. To lose Ryza would be to lose a font of irreplaceable knowledge, and so its defence is written into the strategic scripture of the Priesthood as an article of faith, to be maintained until the machines themselves fall silent.