Isstvan System

The Isstvan System is the eight-planet Ultima well where the Horus Heresy stopped being a rumour. Isstvan III was virus-bombed by four Legions hunting their own loyalists; Isstvan V was the drop site where Ferrus Manus died and three loyal Legions were butchered by four more supposed friends.

Isstvan Extremis held the system's augury net until it went silent. Gas giants, mining outposts, and a dwarf world fill the rest of the chart, none of them famous except as scenery for those two massacres. Later loyalist recon found wreckage fields and unanswered status flags. This is not a living Imperial recruiting system; it is a crime scene the Imperium never cleaned.

The Isstvan System still matters because every later civil war in the setting points back to this well. Unofficial fan maps keep the Isstvan Sector parent and do not fold III and V into separate systems.