Ultramar is the realm of the Ultramarines, a cluster of worlds in the Ultima Segmentum that stands as perhaps the most stable, prosperous, and well-governed domain in the entire Imperium. Unlike most Space Marine Chapters, who hold only a single fortress-world, the sons of Guilliman rule an entire interstellar kingdom of some five hundred planets, a legacy of their primarch's genius for statecraft.
Governed according to the principles their primarch set down after the Horus Heresy, the worlds of Ultramar enjoy a standard of order, justice, and civic life almost unknown elsewhere. Its citizens are educated and dutiful, its cities clean, and its planetary defense forces trained to a standard that rivals many armies. From these worlds the Space Marines draw recruits raised from birth to admire the ideals of the Chapter that protects them.
At the heart of the realm lies Macragge, the capital world and seat of the Chapter's rule. In recent times Ultramar has weathered invasion by the forces of Chaos and the return of its resurrected primarch, who now governs the wider Imperium from afar while his domain endures as a model of what humanity might achieve. Ultramar remains a rare light in a dark galaxy, its very existence a quiet rebuke to the cruelty and decay that grip the worlds beyond its borders.