The Burning of Prospero

Prospero is the only major “loyalist” operation that works strategically for Horus. The chain is rigid: Nikaea banned psychic powers → Magnus breaks the ban in order to deliver a warning → a breach beneath the Palace → the Writ of Censure → Russ receives the order to “bring them in”, Horus whispers “destroy”. Operationally this is not a duel between equal Legions. The Thousand Sons are bound by the edict and by the pride of a primarch who, to the last, does not raise the shields. The strike group is the VI Legion, the Custodians and the Sisters of Silence: an anti-psychic package. The operation has to be read through two systems at once: Prospero burns while Terra is already bleeding in the Webway. The Wolves’ losses are disputed in number, not in fact. Magnus goes to Tzeentch not because he wanted to be a traitor but because the Imperium left him nothing else. Two books, two truths; the atlas holds a single event.

Attackers: the VI Legion, the Custodians, the Sisters of Silence, attached Titans, forces of the Mechanicum and the Imperial Army — and about 5,000 Sons of Horus, whose presence is in itself evidence that the order was swapped. Defenders: the XV Legion (~62,000 on the planet), the Prospero Spireguard and the Tizcan militia, psychic technology, brotherhood cults, automata. Numerical superiority lies with the attackers; qualitative superiority with the psykers — until the Nulls step in.

Strikes the Thousand Sons from Terra’s equation as a loyal force and chains the Emperor to the Golden Throne for the whole of the Heresy.