Segmentum Ultima is the largest of the five great divisions of the galaxy, the segmentums, and it’s the one that covers the entire eastern span of Imperial space. If you’ve heard of Ultramar, the Tau Empire, or the Eastern Fringe, you’ve already brushed against it. It’s also the segmentum hit hardest by the Great Rift, with its northern half cut off inside Imperium Nihilus.
What segmentum ultima actually is
The Imperium splits the galaxy into five segmentums for administration and war. Ultima is the biggest by a wide margin, sitting east of Terra and running out toward the galactic edge. Its Segmentum Fortress, the main naval and command hub, is at Kar Duniash.
Because it’s so vast, Ultima holds a huge spread of factions, cultures and threats. It’s less a single region and more a continent-sized theatre of war with dozens of sub-theatres inside it.
The big players inside it
Ultramar, the Ultramarines’ realm, sits here, along with Macragge and the other Ultramar worlds. The Tau Empire is also in Ultima, which is why so much of the Imperium’s contact with the T’au happens on this side of the galaxy.
The Eastern Fringe runs along Ultima’s border, and it’s the frontier where the Imperium meets xenos empires it can’t easily crush: T’au, Tyranids, Necrons and worse.
- Ultramar and the Ultramarines
- The Tau Empire and its sept worlds
- The Eastern Fringe
- Major Ork empires like Charadon and Octarius
Worlds worth knowing
Ultima’s world list reads like a who’s who of 40k. Macragge, Baal, Catachan, Chogoris, Prospero, Nocturne, Ryza, Metalica and Vior’la all sit inside it, along with the Tau home world T’au and the Tau septs of Bork’an, Dal’yth and Vior’la.
There are also regions rather than single planets: the Sautekh Dynasty’s space, the Red Scar, the Pariah Nexus, and the Maelstrom warp storm. The Maelstrom alone has shaped centuries of Imperial and Chaos activity in the region.
| World or region | Why it matters |
|---|---|
| Macragge | Home of the Ultramarines and capital of Ultramar |
| T’au | Tau home world and heart of the Tau Empire |
| Baal | Blood Angels home world, badly hit by Hive Fleet Leviathan |
| Catachan | Death world famous for its Catachan Jungle Fighters |
| Prospero | Thousand Sons home world, destroyed in the Horus Heresy |
| Maelstrom | Major warp storm and long-running Chaos threat |
How the Great Rift changed it
After the Thirteenth Black Crusade and Guilliman’s return, the Great Rift tore the galaxy in two. Much of northern and northeastern Ultima ended up on the wrong side, stranded inside Imperium Nihilus.
That split matters because it cut off whole sectors from Terra’s authority, made warp travel far more dangerous, and left loyal worlds to fend for themselves. For Ultima, it turned an already huge segmentum into two very different problems.
Key facts
- Segmentum Ultima is the largest of the Imperium’s five segmentums, covering the galaxy’s eastern span.
- Its Segmentum Fortress is at Kar Duniash.
- It contains Ultramar, the Tau Empire and the Eastern Fringe.
- Macragge, Baal, Catachan, Chogoris, Prospero and T’au are all inside it.
- After the Great Rift opened, much of northern and northeastern Ultima was cut off inside Imperium Nihilus.
FAQ
Which segmentum is the largest?
Segmentum Ultima is by far the largest of the five. It covers the eastern span of the galaxy, from near Terra out to the Eastern Fringe.
Where is the Segmentum Fortress for Ultima?
Kar Duniash serves as the Segmentum Fortress, the main command and naval base for the region.
Is the Tau Empire inside Segmentum Ultima?
Yes. The Tau Empire sits within Ultima, which is why most Imperial contact with the T’au happens on this side of the galaxy.
What is the Eastern Fringe?
It’s the frontier along Ultima’s edge, where the Imperium meets xenos powers like the T’au, Tyranids and Necrons, and where its grip is weakest.