Overview
The Realm of Ultramar is a stellar region rather than a single planet, noted for relatively ordered worlds within an otherwise brutal Imperium.
Its approximate ring marks a political and military idea: a realm that can coordinate defense across multiple systems.
That coherence becomes even more valuable when the wider galaxy loses reliable connections.
M41 and M42 status
Stellar realm of ordered Imperial worlds.
Guilliman's restored Five Hundred Worlds; a Sanctus bastion held through the Plague Wars.
Timeline
Realm-wide audits coordinate naval, civil, and chapter-linked defenses.
Regional governors increase reserve stores for eastern incursions.
Rift disruption tests the realm's ability to coordinate under stress.
Indomitus authorities use Ultramar as a model for restored order.
The Plague Wars: Mortarion's Death Guard and Ku'gath's plague legions invade Ultramar, fought to a standstill after Guilliman returns from the Battle of Raukos.
Explore the surrounding galaxy
Cartographic positions and several administrative details are intentionally approximate where published Warhammer sources conflict or provide no canonical coordinate system.