Isstvan System

The Isstvan System is an eight-planet system in Segmentum Ultima where the Horus Heresy became open warfare, at Isstvan III and Isstvan V. It is not an active Imperial recruiting system. It is the site of two massacres that the Imperium never cleared.

Four Legions bombarded Isstvan III with virus weapons in order to destroy the loyalist elements within their own ranks. Isstvan V was the drop site where Ferrus Manus died and where three loyal Legions were destroyed by four others they had regarded as allies. Isstvan Extremis held the system’s augury net until it fell silent. The remaining bodies, which include gas giants, mining outposts and a dwarf world, are notable chiefly as the setting for these two events. Loyalist reconnaissance sent later found wreckage fields and unanswered status flags.

The Isstvan System remains significant because later civil wars in the setting trace their origin to it. Unofficial fan maps retain the Isstvan Sector as its parent region and do not treat Isstvan III and Isstvan V as separate systems.