Segmentum Solar is the central of the five vast administrative regions into which the Imperium divides the galaxy, and the most sacred of them all, for it contains the Sol System and Holy Terra at its very heart. Radiating outward from the Throneworld, it forms the core of the human dominion, the region from which the Emperor's authority first spread and around which all the others are arranged.
As the seat of Imperial power, Segmentum Solar is among the most densely settled and heavily defended regions in the galaxy. It encompasses countless ancient and important worlds, including sacred Mars and the great institutions of the Adeptus Terra, and its systems are laced with fortresses, shipyards, and the accumulated infrastructure of ten thousand years of rule. To govern from here is to govern from the center of everything.
The segmentum is administered from Terra itself, and its strategic and spiritual importance is beyond measure, for it is the anchor of the entire Imperium. The loss of any part of it would strike at the very foundations of human power. Rich in history, dense with worlds, and guarded with a vigilance found nowhere else, Segmentum Solar is the beating core of a galaxy-spanning realm, the hub from which the spokes of humanity's fractured empire extend into the dark.