The First Investigation

At Ullanor the Emperor proclaims Horus Warmaster and returns to Terra, to the Webway project. Read the map as a poster and this is a golden parade. Read it as a staff diagram and it is the moment when the centre of gravity of power slides from Terra onto a single fleet. Every later betrayal exploits that gap: the Father is busy with another project, and the son has been given the legitimacy to command his brothers. Do not read “Horus was bad from birth”: in 000.M31 he is still the Imperium’s finest instrument.

Remarkably few events lie between the Triumph and the wound of the anathame. This matters methodologically. The Heresy did not “build up for ten years on every front” — it flared up in a single body and only then made use of lodges that were already in place. Scroll through those four years as one continuous strip and the eye grows used to the motion and takes Davin for “just another frame”; step to it directly and the ritual feels like a rupture.

At Isstvan III Horus, Angron, Mortarion and Fulgrim land the loyal companies of their own Legions and burn them with virus bombs. The line-up of the sides here is a trap for the newcomer: the “loyalists” are not Legions VII and XIII but Loken, Tarvitz, Torgaddon and Garro within those same Legions XVI, III, XII and XIV. The very same XVI Legion stands in both columns. That is a civil war, not “reds against blues”.

The first wave is the X, XVIII and XIX. The second, the “reinforcement”, is the IV, VIII, XVII and XX: the Iron Warriors, Night Lords, Word Bearers and Alpha Legion. Look only at those numbers and the drop site in 006.M31 is a cauldron, not a “battle of two sides”. Three Legions are struck from the war as strategic quantities. The second wave was believed because the doctrine of the Great Crusade made no provision for a primarch betraying a primarch.

Look at Calth alone and the Word Bearers “lost”: Guilliman is alive, the poisoned Veridia strikes at the XIII, but the Legion is not destroyed. Note the command: the strike is led by Kor Phaeron and Erebus, Lorgar himself is present in person, and after Calth he leaves with Angron on the Shadow Crusade. Armatura and Nuceria show that the XVII won the war in the east even while losing the orbit. The Ruinstorm subtracts Ultramar from the Siege. This is the atlas’s main exercise: never read a famous name without its corridor.

The other investigations — the fall of Horus, the geometry of Isstvan V, how the East was subtracted, the Angel’s path — are built in the same way: a date, a system, a thesis, “how to look”. A step can be interrupted: look into the dossier of a system or a primarch and return to the same date. The cheapest investigation of your own is to ask which Legions are missing from Terra in 014.M31. That too is a question — and it is the map that answers it, not the text.