Isstvan III

Isstvan III is the world where Horus openly revealed his rebellion, through an attack by four Legions on their own loyalists. The world has remained under quarantine since those events.

Four Legions used virus bombs against their own loyalists, ignited the atmosphere, and then spent three months hunting survivors through the Choral City. Twelve billion died in the opening attack. Eidolon led the Emperor’s Children in the killing, while the Eisenstein escaped the destruction in order to warn Terra.

The engagement marked the point at which Horus ceased to conceal his rebellion. Iacton Qruze left aboard the Eisenstein for Terra, and Torgaddon and Horus Aximand, known as Little Horus, were associated with both sides of the betrayal. Isstvan III has since been maintained as a quarantined world.