Macragge System

The Macragge System is the capital star system of Ultramar and the Ultramarines' home well, a mountain-world gravity pocket whose Fortress of Hera still anchors the Five Hundred Worlds. Macragge itself is the seat; moons and sister rocks such as Formaska, Laphis, Ardium, Thulium, and Nova Thulium share the charted heart of Guilliman's civilisation.

Hive Fleet Behemoth died on this doorstep in the Battle of Macragge. The Heresy mostly missed the capital even while Calth and the Shadow Crusade burned the rest of Ultramar, and later Black Legion and Death Guard wars have all treated Macragge as the flag worth taking. Calgar's title Lord of Macragge is a system job, not a city job.

The Macragge System still matters because Ultramar without this well is just a collection of good planets. Unofficial fan maps keep the ultramar-subsector parent and leave Calth in its own Veridian well.