Luna is the traditional name for the moon of Terra which the Imperium of Man classifies as both a Dead World and a Civilised World that is home to billions of people in hive cities built below the surface of the lunar regolith.
Humans first landed on Luna in the year 969.M2, making it the first world ever explored by Mankind in the ancient past. In the subsequent centuries, it was one of the first worlds colonised by humanity, who erected great domed cities above and below its airless surface.
Luna became a centre of advanced biomedical research and zero-gravity manufacturing during the Age of Technology, when it was the home of the Selenar gene-cults who saw the perfection of advanced genetic engineering techniques as a necessary component of a faith similar in some ways to that of the Cult Mechanicus of the Mechanicum of Mars.
The Emperor of Mankind conquered and united Old Earth during the Unification Wars in the middle of the 30th Millennium and then sent His forces to occupy the human colonies on Luna. The technology and resources of the conquered Selenar gene-cults were used to vastly accelerate the production of new Space Marines for the burgeoning Legiones Astartes.
Luna later became the site of many of the most potent static orbital defences used to protect Terra from enemy attack, a role it still plays in the late 41st Millennium.
Luna was Terra's only natural satellite. Although not the largest natural satellite in the Segmentum Solar, it is the largest relative to the size of the planet that it orbits.
Luna is in synchronous rotation with Terra, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters.
Once, the satellite had been a mottled stone wasteland where humans had ventured in their first infantile steps away from their birth world. They had built colonies there, testing their mettle in the pitiless cold of the void in preparation for future voyages to other planets, but as Terra's people had advanced, Luna had become little more than a way station, a place to pass by on the journey to the interplanetary -- and later, interstellar -- deeps.
This age of exploration and advanced technology came to an end with the coming of Old Night, the chaotic and highly fragmented period of human history between the 25th and 30th Millennia.
By the end of the Age of Strife, Luna had become the bastion of a conglomeration of resurrectionist gene-cults known as the Selenar, whose members believed that human nature was both fractal, fractured and transcendent.
To them, the true nature of Mankind was visible in the flesh and mind of the individual, but each person was an echo of archetypes that persisted throughout human existence. Each Selenar gene-cult clung to a different set of archetypes: some represented them as anthropomorphic figures, some as numbers, and some as symbolic systems.
Shot through with low occultism, most fell short of deification, but all pursued understanding through their craft of gene-forging. Each cult member was a product not of random breeding, but creation by the cult's gene-wrights according to formulae born in the Dark Age of Technology.
Resurrected in body time and time again, they attempted to reach a true personification of a single human archetype. In their subterranean complexes beneath the lunar regolith, the cults were powerful, insular and resistant to the Imperial Truth.
Such resistance was hardly a novelty, and would normally have been dealt with in the usual manner -- by obliteration. The fact that the gene-cults had something that the growing Imperium needed complicated that position.
Clouded as it might have been by occultism, the gene engineering techniques of the Selenar Luna cults was unequalled save within the Emperor's own facilities on Terra. With Terra teetering on the edge of complete Unification by 798.M30, the conquest of the Sol System and the galaxy beyond beckoned.
For the Great Crusade there would need to be more and more Space Marines. The Terran gene-engineering facilities would not be able to cope with such a huge increase in the creation of recruits for the Space Marine Legions, so the newborn Imperium of Man needed Luna's wealth of gene-craft and technological capacity added to its own.
But the Selenar gene-cults would not bow willingly to the hunger of the new-born Imperium, and had fought off the machinations of Terran warlords and Martian Magi in the past. The Selenar had received Imperial ambassadors with courtesy, but always answered their offers, threats and entreaties with silence.
As the threats began to outnumber the offers, the Luna cults began to turn away the ambassadors and gird themselves for war. Normally highly factional, the possibility of Terran domination overcame all doctrinal disagreements between the Selenar cult matriarchs and gene-wrights -- they would resist the Imperium together and without limit.
The final Imperial deputation to Luna was returned to Terra as a still-screaming soup of fused liquescent flesh in the dead shell of their shuttle. So it was that the Emperor finally ordered Luna to be pacified by the sword, their superstitious beliefs cast down before the Imperial Truth and their gene-craft yoked to the needs of the Imperium.
As such, Luna would become the site of the first off-world Imperial Compliance action ever undertaken by the early Astartes Legions, even while the Unification Wars were still raging on Terra before the year 800.M30.
First Pacification of Luna
To the task of conquering Luna, the Emperor set three of His newborn Space Marine Legions most suited to this purpose on what some Imperial chroniclers name as the first true battle of the Great Crusade. The combined force of the VII, XIII and XVI Legions (later named the Imperial Fists, Ultramarines and Luna Wolves) lifted from the surface of Terra in a scattering of rocket flame. The as-yet-unnamed XVI Legion had been chosen to serve as this Space Marine force's vanguard, and had brought its full strength to bear.
Cutting power to their assault craft, the Astartes of the XVI Legion drifted silently towards Luna from Mankind's birthworld through the void like arrows fired into the night. As the smaller wave of assault craft belonging to the VII and XIII Legions approached the airless world, the Selenar defensive weapon systems embedded in Luna's surface lashed the oncoming Imperial force.
The XVI Legion's assault craft, unlooked for and unseen, struck their targets like a dagger in the night. Within six solar hours of the first shot being fired, Luna had been pacified and brought into Imperial Compliance, the first off-world conquest of the Imperium of Man.
Faced with annihilation, the surviving Selenar cultists bent the knee instead, their surrender communique transmitted to Terra calling for the Emperor to "call off his wolves." Broken and humbled, the enslaved gene-wrights of Luna would help forge the next generation of Space Marine who would carry out Mankind's conquest of the stars. As for the XVI Legion, they had earned their name -- the Luna Wolves.
For a time in the Age of Strife when Terra was engulfed in war and blood, the Moon had become desolate and empty once again despite the small population of Selenar, but after the rise of the Emperor and its conquest by the Imperium, Luna knew a rebirth. Waxing and waning, the satellite came full circle as the Age of the Imperium brought it new life.
Bisecting the grey stone sphere across its equator lay a man-made valley many kilometres wide. This was "the Circuit," an artificial canyon that laid open the rock and stone beneath the dusty lunar surface. All along the length of the chasm lay gateways into the Moon's interior, vast doors to the honeycomb of spaces carved by Mankind in the heart of Luna.
The ancient, dead boulder of the Moon became the largest military complex ever built by humans. A vast orbital shipyard for the armada of the Imperium, thousands of starships from the smallest shuttle to the largest Battle Barge, were built and maintained there, and across the face of the Far Side there were complex stations for observation of the great void beyond.
Port Luna was the cold, stone heart of humankind's great fleets. The satellite was as much a weapon as it was a safe harbour. Much of the metals mined from the Moon's heart and the rock from the Circuit's excavation had been employed by the Emperor's most-skilled engineers, fashioned into a synthetic ring that girdled the planetoid.
The vast, grey hoop held batteries of Lance cannons and docking bays for more warships. Wherever the light from Luna fell, those who saw it could sleep soundly knowing the ceaseless guardian stood to their defence. And beyond it lay the sacred soil of Terra itself.
During this period in the era of the Great Crusade, Luna was home to the Sisters of Silence, known also as the Silent Sisterhood. They were the militant arm of the Adeptus Astra Telepathica and were internally referred to as that organisation's Departmento Investigates.
Their base of operations, the mighty brass fortress-monastery known as the Somnus Citadel, was located on Luna. Within the mighty fortress were multiple tertiary landing ports designed for shuttles deployed aboard the Black Ships, the dread starships that make up the fleet of the League of Blackships, which forms the recruiting division of the Adeptus Astra Telepathica.
The Gene-Seed Crisis
As the Emperor's Wars of Unity broke the bounds of Terra, the pacification of the gene-cults of Luna and the Martian Compact allowed the Imperium to produce and equip new Space Marines at an unprecedented rate, and the Legiones Astartes began to expand to meet the demands of war across the stars. It had been apparent since the beginning of the Great Crusade that the Emperor's great vision of a united humanity free of the shackles of torment wrought by a nightmarish cosmos was threatened by as many enemies within the Imperium as without.
No clearer sign that such hidden foes could strike at the heart of the Imperium occurred than the so-called "accident" that resulted in the gene-seed crisis that was nearly to doom the III Legion (the future Emperor's Children) -- an act which many have since been attributed to the actions of a secret enemy within.
As the gene-forges began to implant gene-seed organs into recruits for all the Legions, a portion of the III Legion's gene-seed reserve was despatched to Luna for establishment there. What happened next is not clear. Some claim the elements of the Selenite cults still resistant to the Imperium hijacked a Defence Laser and destroyed the ship carrying the III Legion's gene-seed, while conflicting accounts recount that the ship lost control and crashed as it was attempting to dock, whilst others claim that it simply vanished.
It would be too easy, in retrospect, to assign hidden conspiracy or malignant agency to this disaster, though this is not a possibility that can be discounted. The loss of the III Legion's gene-seed reserve was a severe blow, but it would not have endangered the Legion's survival if a second calamity had not occurred in quick succession.
The Horus Heresy
During the latter years of the great rebellion known as the Horus Heresy, the Warmaster Horus, first amongst Primarchs and most-favoured son of the Emperor, led his Traitor Legions to the very heart of the Imperium. Possessed as he was, the Warmaster had lost none of his strategic bluntness: crush the heart, and the Imperium could be remoulded as he saw fit in his own warped image.
During the Solar War, Luna was the target of a massive Traitor assault led by the Sons of Horus First Captain Ezekyle Abaddon. During the fighting, Luna's massive orbital defence ring was the target of a kamikaze attack by the Battle Barge War Oath. Abaddon then assaulted the lunar surface and captured the remaining Selenar gene-labs from Loyalist forces.
The Selenar Cults, resentful of their original conquest by the forces of the Imperium two centuries before, chose to side with Horus and shared with him their genetic engineering technology. After the Traitors were defeated during the Siege of Terra, Luna was later reclaimed by the Loyalists early in the Great Scouring.
Due to the resurrected Primarch Roboute Guilliman's efforts to reach Terra through the Webway after escaping from captivity on a Blackstone Fortress in the Maelstrom, Magnus the Red and his Thousand Sons Traitor Legion followed Guilliman's surviving Crusade forces through the Webway to emerge on Terra's moon.
In the subsequent battle, the Chaos invaders were defeated thanks to the arrival of Imperial reinforcements from Terra that included elements of the Imperial Fists, Adeptus Custodes, Battlefleet Solar, the Sisters of Silence and the aid of a troupe of Aeldari Harlequins led by the Shadowseer Sylandri Veilwalker.
The Somnus Citadel
The Somnus Citadel was the headquarters of the anti-psyker Sisters of Silence during the Great Crusade. Based on Luna, it contained launch bays for Black Ships and was an impressive fortress armed with automated gun-drones. In addition, parts of the citadel could be separated and lowered underground in case of attack.
During the early stages of the Horus Heresy, the survivors of the Eisenstein were interred within the Somnus Citadel on the orders of Rogal Dorn after fleeing the start of the Heresy at the Istvaan III Atrocity.
Battle erupted in the citadel when the terminally ill Eisenstein survivor Solun Decius gave himself over to Nurgle to end the pain of Nurgle's Rot that he was enduring. Possessed by a daemon who transformed his body into a mutant abomination, Decius slew numerous Sisters of Silence and his fellow Loyalist Death Guard of The Seventy until he was slain by Nathaniel Garro on Luna's airless surface.
Shortly before the Siege of Terra, the Sisters of Silence abandoned the Somnus Citadel in order to further fortify the Imperial Palace on the Throneworld.
Luna is home to immense planetary Defence Lasers charged with protecting Terra from invasion that are constructed on an orbital belt of defensive platforms that encircle the circumference of the world and is known as "The Ring." Made from rock excavated from Luna itself, The Ring is bristling with countless Lance, torpedo, and Macrocannon batteries.
These defences inflicted savage losses on the invading Traitor Legion fleets of the Warmaster Horus during the climactic stages of the Horus Heresy. After the Horus Heresy, Luna continued to serve as a massive orbital shipyard and the home of immense planetary Defence Lasers intended to serve as one of the final lines of defence for Terra.
It was created from an artificial ring that had been positioned into orbit around Luna after the Imperial conquest composed of metals mined from the Moon's heart and the rock from the Circuit's excavation by the Emperor's most-skilled engineers. Due to the number of Imperial starships constructed at Port Luna, Luna also gave its name to the most common class of Imperial Navy Cruiser, the Lunar-class.
"The Circuit" was the name given to a massive artificial valley that had been gouged into Luna's surface that was home to countless military compounds, command centres, manufactoria, and other facilities designed to aid the war efforts of the Imperium.
Herodotus Omega Dome
During the Great Crusade and Horus Heresy eras, the Herodotus Omega dome represented one of the major settlements of Luna.
The Selenar gene-cult that ruled Luna before the Imperium conquered it had dug a large complex of gene-laboratories out from the lunar regolith beneath this city.
The vaults in this subterranean complex contained several of the Selenar's failed experiments, such as the Space Marine Ur-legionaries. They were also where the fugitive gene-witch Ta'lab Vita-37 had hidden the Selenar's greatest artefact, the so-called Magna Mater.
During the Siege of Terra at the end of the Horus Heresy, after the Traitor forces of the Warmaster Horus had conquered Luna, Ta'lab Vita-37 enlisted the aid of the crew of the Iron Hands Strike Cruiser Sisypheum to help her keep the artefact from falling into the Traitors' hands.
During the battle that ultimately ensured between the forces of the Sons of Horus and the Loyalists of the Sisypheum, the dome was destroyed.
- Codex: Space Marines (4th Edition), pp. 13-14
- Realms of Chaos: Slaves to Darkness (1st Edition), pg. 241
- The Horus Heresy - Book One: Betrayal (Imperial Armour) by Alan Bligh, pp. 80-81, 104
- The Horus Heresy - Collected Visions, pg. 354
- The Flight of the Eisenstein (Novel) by James Swallow, Ch. 15
- The Solar War (Novel) by John French, Chs. 16, 20
- Gathering Storm - Part Three - Rise of the Primarch (7th Edition), pp. 72-85
- The Buried Dagger (Novel) by James Swallow, Ch. 2
- Siege of Terra - Sons of the Selenar (Novella) by Graham McNeill, Chs. 8-11