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Ancient Departmento Cartographicae map depicting the sub-sector of the Coronid Reach.

The Coronid Reach is a sub-sector and region of Imperial space situated at the borders of the Segmentum Obscurus and the Ultima Segmentum. Located to the galactic northeast of the populous worlds of the Manachean Commonwealth, the Coronid Reach is delimited to the galactic west by the forbidden Coronid Prohibition Zone and to the east by the desolate interstellar wilderness known as the Frost Gyre.

It is rightly regarded as the furthest anchor point of Imperial civilisation and the very edge of Imperial territory before the dark frontier of intergalactic space. Home to the populous worlds of the Cyclops Cluster and the Manachean Commonwealth as well as the more baleful Grail Abyss and Cyclothrathine Holdfast, the Coronid Reach is the last region to make up the sector that was once known as the Coronid Deeps or Coronid Thule, sometimes also called the Thule Sector, which has ceased to exist since the days of the Horus Heresy.


The Coronid Reach is a vast realm that constitutes the northern frontier of the Imperium. Although counted as an independent division of such neighboring realms as the Manachean Commonwealth, it has no true administrative capital, the entire Reach being somehow overshadowed by the influence of the principal power in this region, the Agathean Domain.

Therefore the history of the Coronid Reach pretty much confuses itself with the history of the 60th Expeditionary Fleet and the conquest of the world of Agathon, although the first world to have been colonised was in fact the later Agri-world of Numinal. Hemmed in by two hostile regions of space, human civilisation expanded along the stable warp-routes that originated at Numinal before spreading to the rest of the Reach.

The isolation of the worlds of the Coronid Reach would prove both a boon and a curse as during the dark days of the Horus Heresy the entire region was entirely cut-off from other Imperial territories and was subjected to the baleful intentions of the Traitor Forge World of Cyclothrathe. However, the Reach's isolation would also safeguard it from the Warmaster Horus' direct intentions, leaving only vassal or second-line Traitor forces to threaten them. In the first years of the galactic civil war, resistance would be fierce, particular in the Agathean Domain.

The Coronid Prohibition Zone

An astro-navigational hazard of considerable size and uncertain borders, the Coronid Prohibition Zone, also commonly known as the Coronis Abomination and popularly to the members of the Navis Nobilite as the "White Darkness," borders the central northern edge of the Coronid Deeps region. By popular wisdom among the void-faring, it presents the most obvious reason for the dividing point of the ancient Segmentum Obscurus and Segmentum Ultima in human stellar carthography.

This apparently all-but-empty region of space holds up neither spectacle nor warning to either the naked eye or Auspex, while in the Warp it apparently represents itself as a "white out" to the Navigator's vision, akin to the blindness a man might encounter if trapped in a blizzard -- a literal "nothingness."

The cause or consequence of the danger this region entails remains entirely unknown, and long-range astronomical auguries indicate that only a handful of solitary and unremarkable stars may be found within its otherwise empty volume, sitting as it does between the outermost galactic arm of our galaxy far from the dense clusters of stars which make up the celestial corpus.

Voidships that pass into or through the prohibition zone, either via realspace or the Warp, seldom return, and those that do often have been found to suffer severe chrono-distortion and displacement, itself often leading to fatal consequences for both the living and their machines, as well as those who came into direct contact with them.

By direct order of the Emperor, the Coronid Prohibition Zone was established, explicitly forbidding deliberate entry to this mysterious and deadly region of space. A number of autonomous armed watch stations were created roughly proscribing the zone's borders. These stations establish and police the cordon around the zone, and dispatch Warp-capable hunter-killer Golem-ships to engage and destroy any vessel or object detected leaving the zone.

Planets and Domains of the Coronid Reach

  • Agathean Domain – At the heart of the Agathean Domain lies the sprawling Hive World of Agathon, the most populous planet in the entire Coronid Reach. Conquered by force of arms during the latter days of the Great Crusade, Agathon has since become a highly martial society; most of its inhabitants descend from the original mortal soldiers of the 60th Expeditionary Fleet and have served in the famed Agathean Cohorts. Agathon's military might is such that it subjugated nearby worlds like Legatus and Othion and established its own independent domain within the sub-sector. It is the local political, industrial and military power and dominates the Coronid Reach in every other regard. It is fortunate for the Imperium that Agathon's ruling dynasty, the MaSade, proved fervent supporters of Unity and the Imperial Truth. During the Horus Heresy, it was through Agathon's and Ireton MaSade's efforts that the Coronid Reach did not fall entirely under the sway of the baleful Cyclothrathe Mechanicum.
  • Antayka
  • Bitter Hold
  • Cerada Trinity – The Cerada Trinity is an alliance of three neighboring star systems to the galactic east of Numinal that derived their name from the Cerada Nebula in which they are located. The Trinity consists of three very different worlds: the Civilised World of Cerada Primus, the Mining World of Cerada Secundus and lastly the Feral World of Quavausari. The Trinity has long been plagued by pirate activities, preying upon the interstellar traffic between the colonised planets Cerada Primus and Secundus. The wealth and power of these two worlds has thus far been enough to guarantee its independence from the Agathean Domain. The pirates' presence has led the Trinity to invest a sizable portion of its production capabilities in sleek pirate-killer vessels which were unfortunately all lost during the Treachery at Port Maw incident. As for other worlds of the Coronid Reach, the Cerada Trinity came under attack by the Traitor Cyclothrathe Mechanicum early on in the conflict known as the Horus Heresy. Nearly entirely subjugated by 009.M31, the Loyalist victory during the Liberation of Numinal would buy its defenders precious time to reorganise themselves and hold out a bit longer.
  • Garella
  • Numinal – The famed Agri-world of Numinal has provided the Manachean Commonwealth with much-needed nutrient import almost since its inception in the early 900s.M30. Being the only dedicated and exploitable Agri-world within the Coronid Reach, Numinal's strategic value was further increased by the nexus of stable Warp-routes originating there and from which every system within the Reach could be joined. It was for this reason that the sub-sector's sole navigational relay was installed on one of Numinal V's moons, turning the Numinal System into the proverbial gateway to the entire sub-sector of the Coronid Reach. All these factors came into consideration when the Traitors of the Cyclothrathe Mechancium attacked the system, Numinal's own defence flotilla having fallen during the Treachery at Port Maw. The Agri-world would suffer harshly under the Dark Mechanicum occupation but would ultimately be freed during the famed Liberation of Numinal campaign which would see the Agathean Cohorts victorious against the inhuman legions of Cyclothrathe Battle-Automata.
  • Vespasia Infernus – The Mechanicum Explorator outpost of Vespasia Infernus is the last known inhabited world in Imperial space before the intergalactic void. Only reachable through one of the minor Warp-routes originating in the Numinal System, Vespasia Infernus is an isolated world that has long since learned to rely on itself.
  • Zarnov – Zarnov is an Industrial World of high standing that lacks the population to be a Hive World. It is an isolated planet situated to the galactic north of the dreaded Coronid Prohibition Zone, where all travel has been forbidden by Imperial Edict and whose borders are being enforced by hunter-killer Golem-ships. The only stable and therefore most travelled Warp-route leads to the distant Hive World of Keopsis in the Grail Abyss.


  • The Horus Heresy - Book Four: Conquest (Forge World Series) by Alan Bligh, pp. 10-11, 24, 40, 73-75, 94