Thoas

Thoas is a tidally locked Ultima world whose pre-Imperial human civilisation poisoned itself, then hosted an Ork empire the Ultramarines burned in the Great Crusade. This pin is the Lord of Ultramar battlefield, not a random Thoas with no Guilliman on the ledger.

The XIII Legion purged neighbouring systems and finished the war here against an Ork seat of power sitting on irradiated ruins. Two moons watched. Unaugmented humans still could not live on the crust. Guilliman's compliance left a dead museum rather than a new tithe world.

Thoas still matters as an early Ultramarines lesson about empires that eat themselves. Unofficial fan summaries keep the Ultima parent and refuse to file the pin as a 40k hive or as a different Thoas in another Segmentum.