Ultramar Subsector

The Ultramar Sub-sector is the charted administrative cube of Guilliman's Five Hundred Worlds, an empire-within-the-Imperium in Ultima Segmentum whose inner systems include Macragge, Konor, Iax, and Espandor. Unlike most Chapter fiefs, this is a whole civilised neighbourhood with its own auxilia, defence fleet, and Tetrarchs.

The Great Crusade grew it; the Shadow Crusade and Ruinstorm nearly cut it off; Imperium Secundus was the emergency state that lived here. Behemoth, Honsou, the Black Legion, and Mortarion's Plague Wars have all tried the same door. Guilliman's return put the old borders back on the table and stationed Shield Chapters across a realm that still feeds itself better than most of the Imperium.

The Ultramar Sub-sector still matters because it is the one Imperial neighbourhood that looks like a working state. Unofficial fan maps keep the ultima-segmentum parent and leave Calth, Talassar, and the rest as child systems rather than flattening Ultramar into Macragge alone.