Ilithyia (officially Cerestne XVII), is a fortress world in orbit of the star Cerestne.

Orbital CharacteristicsEdit

  • Mean Orbital distance: 2,327,000,000 km (15.56 Astronomical Units)
  • Inclination: 1.75° to invariable plane
  • Orbital period: 10012.058 local days (12241.532 Terran solar days/ 33.516 Terran years)

Planetary CharacteristicsEdit

  • Mass: 8.663 x 10^24 kg (1.45 x Terra)
  • Mean Radius: 7098 km (1.11 x Terra)
  • Equatorial Radius: 7106 km (1.11 x Terra)
  • Polar Radius: 7080 km (1.11 x Terra)
  • Oblateness: 0.003661732 (1.09 x Terra)
  • Equatorial gravity: 11.445 m/s/s (1.17 x Terra)
  • Escape Velocity: 12754.41968 m/s (1.14 x Terra)
  • Sidereal day: 105628.911 seconds (29’ 20" 28.911)
  • Solar day: 105639.461 seconds (29’ 20" 39.461)
  • Axial tilt: 15.22937 degrees
  • Albedo: 0.308

Natural satellitesEdit


  • Orbital distance: 504,700 km
  • Mass: 3.242 x 10^20 kg
  • Average Diameter: 774 km
  • Orbital period: 28.05 local days (34.30 Terran).

Erané has no atmosphere and negligible gravity (~0.06 m/s/s) and is uninhabited. Rumours of a small Adeptus Mechanicus facility on Erané have existed for some time, but have always been denied by Mars. Erané’s orbital period is noted to be in a 5:1 orbital resonance with Ilithyia’s larger moon, Scita.


  • Orbital distance: 172,800 km
  • Mass: 1.659 x 10^22 kg
  • Diameter: 2221 km
  • Orbital period: 5.61 local days (6.86 Terran).

Scita has no notable atmosphere. However, having a low gravity of approximately 0.9 m/s/s, Scita was suitable for use to site one of Ilithyia’s orbital ports.

Strong objections were made when the suggestion that Scita should be razed in the same manner as Cerestne XXXII’s Beta moon, and it therefore remains an important defensive location, with most of its sealed enviro-domes still intact.

Artificial satellitesEdit

9,372 minor, 30 orbital defence stations. Ilithyia’s orbital defence stations are repurposed from what remains of the planet’s former 96 orbiting ports. Many transits to the surface involve docking at or orbiting near one of these stations and taking shuttles down, an option that does not involve leaving a lone ship to fend for itself in orbit.


Ilithyia’s surface is approximately 53% water, with the remaining 47% made up by nine continental landmasses, spread over twelve of the planet’s twenty one major tectonic plates. Major seismic events are approximately twice as common as on Terra, although most buildings near fault lines are heavily reinforced against this eventuality.

Prior to 938.M41, with most of the ports in orbit, the surface of Ilithyia was similar to a moderately populated garden world – largely verdant terrain, although with some arid/desert terrain close to the equator and floating polar ice caps. Due to the planet’s tectonic shifts and geological development, the planet has a reputation for being mountainous, with several rocky mountain ranges between intersecting continental plates. The highest recorded altitude on Ilithyia, at 9,721 metres above average sea level, is Kjaro Peak on the Etoe continent, although this is only 39 metres above the summit of Mavant, (located some 873 km to the west, near the intersection of the Etoe and Harana continents).

Since the planet’s militarisation, a generous portion of the planet’s forests have been razed, either to provide land for fortifications or to deny cover to the invading forces.


  • Average Atmospheric pressure: 126671 Pascals
  • Atmospheric composition:
    • Nitrogen: 82.47%
    • Oxygen: 16.53%
    • Argon: 0.88%
    • Carbon Dioxide: 0.07%
    • Other/Trace: 0.05%
    • Presence of low molecular weight gases such as Helium and Neon is marginally higher than Terra.

Despite a lower fractional percentage of oxygen compared to the traditional Terran atmosphere, a higher overall atmospheric pressure means that partial oxygen pressures are similar. Similarly to on Terra, this balance appears to be defined by factors such as flora proliferation and severe natural fires.

Weather is relatively typical for a temperate world, but has only rare extremes. The arrangement of the planet's continents gives it relatively small oceans compared to many other worlds, reducing the frequency and intensity of ocean storms, which usually break up quickly on reaching land.

Average global temperatures are approximately 284 K, marginally below Terra. Seasonal variations are lower than Terra, due to Ilithyia’s lesser axial tilt.

Flora and FaunaEdit

Life on Ilithyia appears to have undergone at least two separate abiogenesis events, as the efforts of the Adeptus Mechanicus cannot reconcile Ilithyian species into fewer than two phylogenetic trees.

The most evolutionarily successful of the world’s native fauna are found in the class of Enstrodyna (In the dialect of the original settlers: Ens "internal"; tro, a plural prefix; dyna "jointed" – equivalent to "many jointed endoskeleton"). Notable for twin elbows/knees per limb (although on some species, the intermittent bones are very short or vestigial, which may mean they appear to have only one joint), endothermic metabolisms, hairless bodies and having two forms of perspiration – one, thick and mucus like, to seal in heat, and a second closer to its function in Terran primates, to lose heat.

Loosely equivalent in the Ilithyian biosphere to Terran mammals, this class is similarly versatile, with different orders and species capable of surviving in almost all of Ilithyia’s environments.

Flora is remarkably similar to Terran, although the process of photosynthesis instead relies on the chemical Caphryin, which makes imported flora easily visible amongst the distinctive darker yellow/green colour of Ilithyian flora.


  • 865.M32: Cerestne System discovered as part of Nakt Crusade
  • 873.M32: Ilithyia discovered in orbit of Cerestne.
  • 880.M32: An Explorator expedition declares Ilithyia habitable to humans.
  • 902.M32: First colony ship arrives, largely drawn from the civilian populations of neighbouring subsectors. In this respect, Ilithyia is unusual amongst the Cuir subsector, where most worlds were colonised by the Imperial Guard regiments that conquered them.
  • 902.M32 – 679.M33: Moderate urban development and the start of the political manoeuvring that set up the ruling classes – some families from which still exist to this day.
  • 679.M33: Scaro passage first discovered by Navigator Scaro DeVega.
  • 685.M33: Passage officially recognised as a stable route to the Alykia sector. Added to most Imperial maps.
  • 693.M33: Heavy development of orbital stations begins. Continues to 6th century M34.
  • 712.M33: Hydrogen mining process begins on Cerestne XXXII.
  • 762.M33: Ilithyian tithe grade increased. First Ilithyian regimIent of the Imperial Guard formed.
  • 007.M34-022.M34: Civil war sees the ruling Delvane family replaced by the Unrick clan.
  • 825.M34: The attempt to introduce a specific currency for the Cuir subsector causes mass confusion in Ilithyian ports. The attempt is later abandoned.
  • 507.M35: Jante-class transport miscalculates warp jump and collides with northern polar ice cap. The Ilithyian climate is disrupted for several decades. Vnral warp jump point declared an unsafe distance from the planet and removed from warp maps.
  • Early M36: Age of Apostasy. Unrick family replaced by Inram, rising to power in support of Goge Vandire. Following Vandire’s death, Delvane family returns to power.
  • 324.M37: Scaro passage enters a twelve year hyperactivity, with journeys taking less than a third of the regular time. Ilithyian ports overwhelmed during this time.
  • 272.M38: Upsurge of economics in Alykian sector provides another unexpected boost to Ilithyian trade.
  • 962.M38: Delvane family killed by unknown virus – suspected genengineered.assassination weapon. Valpen family takes governorship.


  • 341.M41: Archeological evidence suggests a state of previous Human/Xeno co-habitation on Ilithyia.


  • 915.M41: Scaro passage begins shipping millions of soldiers a year into the Alkyia sector in response to the Warlord Imylosst’s invasion. Commercial freight begins dwindling over next two decades.
  • 935.M41: On a wave of public opinion, the relatively unknown Natalia Krux deposes Horiatio Valpen from governorship. Immediately begins developing Ilithyian defences.
  • 936.M41: Gragon system at far end of Scaro Passage captured by Ruinous Powers.
  • 938.M41: State of war declared. Ilithyian tithe grade reassigned as Aptus Non.
  • 940.M41: Troops from Pexirian and Theklian regiments deployed on Ilithyia.
  • 942.M41: First recorded contact with Chaos forces in Cerestne system.
  • 968.M41: Between the increased deployment of external forces and additional militarisation, number of Imperial troops on Ilithyia is doubled within six months.
  • 970.M41: Attempt by the collaboration of one thousand navigators to seal the Scaro Passage fails.
  • 988.M41: Portions of the Solemne Titan Legions arrive on Ilithyia.
  • 001.M42: Inquisitor Kalius Solnes takes charge of Inquisition contingent.
  • 427007.M42: Corporal Aderyn Aeslin first arrives on Ilithyia.
  • 515011.M42: Corporal Aderyn Aeslin dies after a lone defence of Zulu position.
  • 519011.M42: Corporal Aderyn Aeslin resurrects.
  • 825011.M42: Scheduled date for the High Conclave at the Inquisition fortress on Tigguo Cobauc.


Approximately 3,100 million citizens; 730 million auxiliary troops. 44% of the citizen population is under arms.

Given the number of immigrants to the world over the millennia, Ilithyians closely conform to Carthaxian averages for measurable traits such as height and muscle mass. The only notable deviation is the comparative rarity of light eye and hair pigments.


With a population that spans six of Ilithyia’s eight continents and with the degrees of planetary immigration common in the past, there are few sweeping summaries that can be made of its once rich culture.

Ilithyia has felt the attrition of war like everything else, and many nuances of its past have been lost in only a short few decades. However, as a relatively young fortress world, some elements of its old culture still show through.

Society is still stratified like many Imperial worlds, although many of the world’s former noble families have left the planet entirely. Only a few remain, most with strong ties to the military. It is typical for the first in line to a noble title to take the prefix of "Jun". With the violent situation on Ilithyia, these titles are passed on regularly, either through the death of the patriarch or former Jun.

Relatively few of the working/fighting classes can still remember a pre-war Ilithyia, so the financial divide that once existed is largely forgotten by those unable to afford rejuve.

The lower classes are noted for their pride in the fact that when the call of war came, their world was not found wanting and that they have thus far held over three times as long the entire Alykian sector.

Note to visiting Inquisitors: Observations of Ilithyia's success as a defensive location being more dependent on prior warning and the depleted resources of traitor warships after a many month journey than the courage of Ilithyians are noted to antagonise the local population.

Planetary CapitalEdit

The heavily fortified planetary capital of Ilith Nova is found in the southern hemisphere, with an approximate population of 17,000,000. Most centres of the government and major Imperial organisations can be found here.

Its defensive features include a thick rockrete perimeter wall mounted with thousands of Earthshaker turrets, making ground assaults on the city near impossible, although this defining boundary has also forced the city to start developing upwards, turning it into something of a proto-hive.

Built in to the city wherever space allows it, the network of massive anti-air turrets are said to have the firepower and targeting abilities to be capable of destroying even Astartes drop pods in descent (although the veracity of this claim is questionable). This formidable defence is supported by a large compliment of Imperial Navy fighters.

To date, only the assault of the traitor Warlord Titan E Tenebris has yet posed a serious threat to the city. One of the Solemne Titan Legions has since been deployed against this possibility.