Horus Heresy · atlas

Campaign · Isstvan System · Segmentum Ultima · 005.M31

The Isstvan III Atrocity

Four Legions land their own loyalists on the pretext of suppressing a rebellion and burn them with the Life-Eater. Garro escapes aboard the Eisenstein. The Heresy becomes open.

Outcome An atrocity. The loyal portions of four Legions are destroyed; the news travels to Terra.

Commanders

Loyalists

Commanders

Traitors

Commanders

Theatre
Isstvan System · Segmentum Ultima
Period
005.M31
Legions
Systems

Analysis

Isstvan III is not a battle for a world but a purge of the command cadre. Horus, Fulgrim, Angron and Mortarion gather those whom the lodges judged unreliable and send them down to “restore order”. The Life-Eater virus bombs were supposed to finish the job within hours; the canon records that they did not: the survivors (Loken, Tarvitz, Torgaddon, Ehrlen) hold out in the ruins of the Choral City for months — the sources give more than two, more often three standard months — while Angron breaks away and goes down against orders. The operational lesson: a conspiracy that cannot kill its own quietly loses surprise against Terra. That is exactly why the Eisenstein matters more than any company on the surface. After the massacre, compromise between the primarchs is dead. The dates in the sources differ; the atlas sets the atrocity at 005.M31 and the escape immediately after it.

Order of battle

Traitors: the XVI, III, XII and XIV (orbit and finishing off), with the XVII involved as architects. Loyalists: the landed contingents of the same four Legions. Fleet: the Vengeful Spirit and the Andronius against a handful of survivors and a single fugitive.

Turning points

  1. 005.M31 The Life-Eater — Isstvan III Atrocity

    A world’s atmosphere becomes a weapon. This is no longer Compliance but an atrocity.

  2. 005.M31 Angron Goes Down — Isstvan III Atrocity

    The Nails break the plan: the purge turns into a protracted assault.

  3. 005.M31 The Eisenstein Departs — Flight of the Eisenstein

    Garro, Keeler, Qruze. Terra will learn. Dorn manages to begin preparing the Palace.

Events of the campaign

  1. 003.M31 Contact Lost with Isstvan Inconclusive

    A Death Guard patrol ship on the edge of the XIV Legion’s fleet intercepted a fragmentary astropathic transmission: Isstvan III was in the grip of a religious revolt under the defector governor…

  2. 005.M31 Isstvan III Atrocity Pyrrhic traitor victory

    Under the pretext of pacifying a revolt, Horus assembled four Legions at Isstvan III — the Sons of Horus, Emperor’s Children, World Eaters and Death Guard — and with Life-Eater virus bombs…

  3. 005.M31 Flight of the Eisenstein Loyalist victory

    Death Guard captain Nathaniel Garro seized the frigate “Eisenstein” and with a handful of loyalists took her out of the Isstvan system.

Significance

The public birth of the Heresy. Four Legions can no longer turn back; the Imperium can no longer pretend that this is the rebellion of a single world.

How to look in the atlas
  • Time slider 5.0…5.4, “Event type” → mass atrocity: Isstvan III will separate itself from ordinary battles.
  • Trace the single arrow leaving Isstvan for Terra — the Eisenstein. It alone works for the loyalists.

Show on the map

Open in the atlas

Sources

  1. Galaxy in Flames (B. Counter)
  2. The Flight of the Eisenstein (J. Swallow)
  3. Forge World Black Book I: Betrayal
Open in the atlas

Permalink: https://astart.es/en/campaigns/isstvan-iii/