The Milky Way Galaxy, commonly referred to as just the Milky Way, or sometimes simply as the Galaxy, is the galaxy that Mankind calls home and in which the Imperium of Man and all of the other starfaring intelligent species known to humanity are located. The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. It is one of hundreds of billions of galaxies in the observable universe. Its name is a translation of the Latin term Via Lactea, in turn translated from the Greek Galaxias, referring to the pale band of light formed by stars in the galactic plane as seen in the night skies of Terra.
Some sources hold that, strictly speaking, the term Milky Way should refer exclusively to the band of light that the galaxy forms in the Terran night sky and the skies of many other settled planets, while the galaxy should receive the full name Milky Way Galaxy, or alternatively the Galaxy. However, it is unclear how widespread this convention is, and the term Milky Way is routinely used in either context.
The stellar disk of the Milky Way Galaxy is approximately 100,000 light-years in diameter, and is considered to be, on average, about 1,000 light years thick. It is estimated to contain at least 200 billion stars and possibly up to 400 billion stars, the exact figure depending on the number of very low-mass, or dwarf stars. This can be compared to the one trillion stars of the neighbouring Andromeda Galaxy. The stellar disc does not have a sharp edge, a radius beyond which there are no stars. Rather, the number of stars drops smoothly with distance from the centre of the galaxy. Beyond a radius of roughly 40,000 light years, the number of stars drops much faster with radius, for reasons that are not understood.
Extending beyond the stellar disk is a much thicker disk of gas. The gaseous disk of the Milky Way has a thickness of around 12,000 light years. The Galactic Halo extends outward, but is limited in size by the orbits of two Milky Way satellites, the Large and the Small Magellanic Clouds, whose perigalacticon is at about 180,000 light years. At this distance or beyond, the orbits of most halo objects would be disrupted by the Magellanic Clouds, and the objects would likely be ejected from the vicinity of the Milky Way.
The Imperium of Man is the dominant power in the Milky Way Galaxy, ruling over more than 1,000,000 settled human worlds that stretch across the entire length and breadth of the galaxy. To effectively govern and protect this vast domain, the High Lords of Terra and the Adeptus Terra have divided the galaxy into five zones of military and political control known in High Gothic as the Segmentae Majoris (sing. Segmentum). Each Segmentum has its own Imperial Navy battlefleet and Merchant Fleet, as well as a Segmentum Fortress or Segmentum Naval Base that forms the base of fleet and military operations for the Imperial Navy and Imperial Guard, respectively, within the Segmentum. The Segmentum battlefleet commanders are known as the Lord High Admirals. The Segmentum Fortress is controlled directly by a high-ranking official of the Adeptus Administratum referred to as the Master of the Segmentum. Although originally intended for purposes of fleet administration and commercial shipping administration at the time of their creation by the Adeptus Terra, the Segmentae have evolved into the primary political administrative divisions of the Imperium, with each one being further comprised of thousands of 200 light-year-square Sectors. The Sectors are in turn made up of Sub-sectors each comprising a cube of space some 10 to 20 light years square. In general, despite actually being a three-dimensional space, Imperial astrocartographers refer to a location in reference to its cardinal direction from Terra. For example, the "Eastern Fringes" of the galaxy in the Ultima Segmentum is located to the galactic "East" of Terra.
The Segmentae Majoris are:
- Segmentum Solar - Located in the Imperium's Centre with Terra at its very heart, the Segmentum Solar's Segmentum Fortress lies at the nexus point of the massive orbital fleet yards of Mars. The Segmentum Solar is home to the very heart of Imperial territory, ancient and very wealthy worlds that have been settled by humanity since before even the invention of Warp-Drive. Many of the Imperium's most important worlds, including the battleground hive world of Armageddon, lie within this Segmentum.
- Segmentum Obscurus - Located to the galactic North of Terra, the Segmentum Obscurus is where the Eye of Terror and the Imperial Fortress World of Cadia are located, making the Sectors of this Segmentum among the most heavily militarised in the Imperium to protect them from the near constant incursions of the Forces of Chaos. The Segmentum Obscurus' primary Segmentum Naval Base is located at the world of Cypra Mundi.
- Ultima Segmentum - Positioned to the galactic East of Terra and the Segmentum Solar, the Ultima Segmentum is by far the largest of the Segmentae and also the least densely populated by human-settled worlds, having long served as the Imperial frontier. The Ultima Segmentum is home to the Ultramarines Chapter's Realm of Ultramar and to the frontier of the Eastern Fringes of the galaxy. It was from the Ultima Segmentum that the first Tyranid Hive Fleets attacked the worlds of the Imperium. The Eastern Fringes are also home to the upstart Tau Empire that has in recent centuries proved to be a durable xenos threat to Imperial control of the region. The primary Segmentum Fortress and Segmentum Naval Base is located on the world of Kar Duniash.
- Segmentum Tempestus - Comprising the territory to the galactic South of the Segmentum Solar, the Segmentum Tempestus, despite its name, is one of the least troubled regions of the Imperium. It is dominated by the political might of the Ecclesiarchy and is home to the second most holy Cardinal World of the Imperial Cult after Terra itself - Ophelia VII. Segmentum Tempestus' Segmentum Naval Base is located in orbit of the world of Bakka.
- Segmentum Pacificus - This Segmentum contains all of the territory located to the galactic West of the Segmentum Solar. Like the Eastern Fringe of the galaxy in the Ultima Segmentum, Segmentum Pacificus is largely frontier territory, lightly settled by humanity in comparison to the other Segmentae. The Segmentum Pacificus' Segmentum Naval Base is located in orbit of the world of Hydraphur.
Little of the vast history of the galaxy has been revealed to Mankind. What is known beyond the dimly-remembered confines of even humanity's own story has largely been drawn by various human scholars and Adepts of the Adeptus Mechanicus from ancient xenos ruins scattered across the stars and the dying Infinity Circuits of shattered Eldar Craftworlds.
Birth of the Star Gods
The birth of the entities known as the Star Gods occurred at the same time as the moment of Creation itself, as they formed from the vast, insensate energies first unleashed by that churning mass of cataclysmic force. In that anarchic interweaving of matter and energy, the sea of stars began to swirl into existence and for an eon the universe was nothing more than hot hydrogen gas and light elemental dust ruled over by the gravitic force of billions of newborn suns. Long before the first planets had formed and cooled, the very first truly self-aware beings emerged, their thoughts encased within the lines of force produced by the plasma and electromagnetic flares of the stars themselves. In later times, these entities would become known as the C'tan, but early in their existence they were nothing like the malevolent beings they would eventually become. They were little more than monstrous energy parasites that suckled upon the solar energies of the stars that had brought them into existence, shortening the lives of otherwise main-sequence stars by millions of standard years. In time, these star vampires learned to move on the diaphanous wings of the universe's electromagnetic flux, leaving their birthplaces to drift through the cosmic ether to new stellar feeding grounds and begin their cycle of stellar destruction once more. Beings of pure energy, they paid no mind to the hunks of solid matter they passed in the vacuum of space, the blazing geothermal fires and weak geomagnetic fields of these nascent planets insufficient to be worth feeding even their ravenous hunger.
The Empire of the Old Ones
Just as the stars gave birth to their children so the planets of the newborn galaxy eventually gave birth to lifeforms composed of matter which began the long evolutionary climb to self-awareness. The first sentient beings of the Milky Way Galaxy known to have developed a civilisation technologically advanced enough to cross the stars was a reptilian race of beings called the Old Ones by the Eldar, who knew them best. They possessed a slow, cold-blooded, but still deep wisdom, having long studied the stars and raised astronomy and physics to such a level that their science and technology appear to humanity like an arcane art. Their understanding of the workings of the universe were such that they could manipulate alternate dimensions and undertake great works of psychic engineering. Their science allowed them to cross the vast gulfs of space with only a single step through the myriad Warp Gates they built to connect the worlds of the galaxy in a vast network much like the Eldar Webway of today, though on a much larger scale. The Old Ones spread their spawn to many places in the galaxy, but they also knew that all life was precious. Where they passed, they seeded new intelligent species and reshaped thousands of worlds to make them their own according to their predetermined environmental and geographic criteria. It is believed by some in the Adeptus Mechanicus that even Terra felt the Old Ones' touch long before humanity's rise to self-awareness, though this notion is considered heretical at best by the Ecclesiarchy.
As the Old Ones spread across the galaxy, younger, fiercer intelligent races struggled upwards in their wake. The Necrontyr were one such species, born on a world scourged by an unstable star that drove their evolution forward with atomic winds, solar flares and plasma storms. What little information the Imperium has on the Necrontyr tells that their lives were short and uncertain, their bodies blighted and consumed at an early age by the terrible cancers and other illnesses linked to the high levels of ionizing radiation given off by their sun. Necrontyr cities were built in anticipation of their citizens early demise, as the living were only brief residents living in the shadow of the vast sepulchres and tombs of their ancestors. On the Necrontyr homeworld, the greatest monuments were always built for the dead, never the living. Unable to find peace on their own world, the Necrontyr blindly groped outward into the universe to explore other stars. Using stasis crypts and slow-moving, sub-light, antimatter-powered torch-ships that were clad in the living metal known as necrodermis to resist the millennia-long journeys through the void, the Necrontyr began to colonise distant worlds. Sometime during their slow expansion, the Necrontyr encountered the Old Ones. The colonisation of much of the galaxy by the reptilian mystics had been immeasurably swifter and more expansive than that of the Necrontyr because of their Warp Gates and mastery of the Immaterium. That, and the Old Ones' incredibly long, if not downright immortal lifespans, kindled a burning, jealous rage in the Necrontyr, which ate at their culture spiritually as much as their physical cancers consumed their bodies. The Necrontyr were astonished to learn that another intelligent species enjoyed such long lives while their own were cut so brutally short. As their surprise turned to jealousy and then hardened into hatred, the Necrontyr turned their entire civilisation towards destroying the Old Ones and all of their spawn across the galaxy.
The War in Heaven
The terrible wars between the Old Ones and the Necrontyr that followed, known in Eldar myth as the War in Heaven, would fill a library in their own right, but the Necrontyr could never win. Their superior technology was consistently outmanoeuvred by the Old Ones thanks to their mastery of the Webway portals and Warp Gates. The Necrontyr were pushed back until they were little more than an irritation to the Old Ones' dominance of the galaxy, a quiescent threat clinging to their irradiated world among the Halo Stars, exiled and forgotten. The Necrontyr's fury was cooled by their long milllennia of imprisonment on their homeworld, slowly transforming into an utter hatred towards all other forms of intelligent life and an implacable determination to avenge themselves upon their seemingly invincible enemies.
From the earliest days of their civilisation, Necrontyr scientists had been deeply engaged in stellar studies to try to understand and protect themselves from their own sun's baleful energies. After long, bitter centuries of searching for some power to unleash upon the Old Ones, the Necrontyr researchers discovered unusual electrodynamic anomalies in the oldest, dying stars of the galaxy. In the complex skeins of the energetic plasma of these suns, the Necrontyr found a sentience that was more ancient than that of any of the corporeal species in Creation, including the Old Ones, entities of pure energy that had spawned during the birth of the stars eons before. These entities had little conception of what the rest of the universe entailed when the Necrontyr first found them, feeding upon the solar flares and magnetic storms of these bloated red giants. Here was the weapon the Necrontyr had long sought to bring about the downfall of the Old Ones, beings they believed were the progeny of the death-god they worshipped.
The power of these star-born creatures was incredible, the raw energy of the stars made animate, and the Necrontyr called them the C'tan or "Star Gods" in their own tongue. The C'tan were dispersed across areas larger than whole planets, their consciousnesses too vast for humanoids to comprehend. How the Necrontyr ever managed to communicate with them is unknown to the Adeptus Mechanicus. Understanding that such diffuse minds could never perceive the material universe without manifesting themselves in a material form, the Necrontyr forged physical shells for the C'tan to occupy, cast from the living metal called necrodermis that they had once used for their colony torch-ships. Fragmentary Eldar legends tell of translucent streamers of electromagnetic force shifting across space as the star vampires coiled into their new bodies in the physical realm across an incorporeal bridge of starlight.
Incomprehensible forces were compressed into the living metal of the necrodermis bodies which the Necrontyr had forged as the full power of the C'tan at last found form. As the C'tan focused their consciousnesses and became ever more aware of their new mode of existence, they came to appreciate the pleasures available to beings of matter and the other realities of corporeal life. The deliciously focused trickles of electromagnetic energy given off by the physical bodies of the Necrontyr all about them awakened a new hunger in the C'tan very unlike the one they had once sated using the nourishing but essentially tasteless energies of the stars.
For their part, the Necrontyr soon fell into awe of their discoveries and the C'tan moved to take control over their benefactors. The powers of the C'tan manifested in the physical world were indeed almost god-like and it was not long before the C'tan were being worshipped as the Star Gods the Necrontyr had named them. Perhaps they had been tainted by the material universe they had become a part of, or perhaps this had always been their nature even when they were bound to the suns they fed upon, but the C'tan proved to be as cruel and capricious as the stars from which they had been born. They soon revelled in the worship of the Necrontyr and feasted upon the life energies of countless mortal slaves.
The Rise of the Necrons
Armed with weapons of god-like power and starships that could cross the galaxy in the blink of an eye through the use of quantum phase technology, the Necrontyr stood ready to begin their war against the Old Ones anew. But the C'tan had another gift for their mortal subjects. They offered the Necrontyr a path to immortality and the physical stability their race had always craved. Their diseased flesh would be replaced with the living metal of necrodermis that made up their Star Gods' own physical forms. Their discarded organic husks would be consumed and their cold, metal forms would then be free to pursue their great vengeance against the Old Ones and the rest of a hateful universe, freed forever from the weaknesses of their hated flesh. Whether the Necrontyr actually realised the price they would actually pay for accepting this pact with the C'tan is not known, but their species was utterly purged, their essences fused with the robotic necrodermis bodies their scientists had crafted through the power of the C'tan. The Necrontyr became the Necrons, cursed to the eternal servitude of their Star Gods. The C'tan feasted upon the entire Necrontyr race's life energies even as they made the transfers, leaving behind only the ghostly echoes of the Necrontyr's consciousnesses. Only a few of the most strong-willed Necrontyr retained their intellect and self-awareness and even they were but shadows of their former selves. purged of so much of what had made them unique individuals.
The Necrons cared not at all for their loss; all that mattered to them was that they would live forever without disease or death as their Star Gods had promised. Only one thing truly remained of the old Necrontyr - their burning hatred for all the other living, intelligent species of the universe. Legions of the undying living metal warriors set out into the galaxy in their Tomb Ships and the stars burned in their wake. The Old Ones' mastery of the Warp was now countered by the C'tan's supremacy over the physical universe and the ancient enemies of the Necrons suffered greatly in the interstellar slaughter that followed.
The Necrons Ascendant
The C'tan now dominated the galaxy. The last planetary bastions of the Old Ones were besieged and the intelligent races they had once nurtured became cattle for the obscene hunger of the C'tan. To the younger sentient species of the galaxy, the Necrons and their Star Gods were cruel masters, callously harvesting their populations at will to feed the C'tan's ceaseless hunger. The C'tan were figures of terror who demanded their adoration and fear in equal measure. For unknown reasons, but probably because their individual hungers for mortal life energies knew no bounds, the C'tan ultimately began to fight amongst themselves for both sport and out of spite as they unleashed destructive forces beyond mortal comprehension. Among the Eldar, an ancient myth holds that their Laughing God tricked the C'tan known as the Outsider into turning on its brothers and beginning their long war for ascendancy. In the course of the C'tan's struggle against one another, whole planets were razed, stars were extinguished and whole solar systems were devoured by unleashed black holes. New cities were built by the efforts of millions and then smashed down once more. As the "red harvests" of the C'tan and their Necron servants grew thin, C'tan eventually devoured C'tan, until only a few were left in the universe and they competed amongst themselves for a long age.
Eventually, even the Old Ones, who had once been defined by their patience and unstoppable will, became desperate in the face of the Necron assault. They used their great scientific skills to genetically engineer intelligent beings with an even stronger psychic link to the Warp, hoping to create servants with the capability of channeling psychic power to defend themselves. They nurtured many potential warrior races, among which were believed to be the earliest members of the Eldar species and many other xenos races, including the Rashan, the K'nib and many others. Millennia passed as the Old Ones' creations finally bore fruit and the C'tan and their Necron servants continued to extinguish life across the galaxy.
The Tide Turns
The Old Ones' psychically-empowered servant races spread across the galaxy, battling the advanced Necron technology with the psychic power of their Warp-spawned sorcery. Facing this new onslaught, the C'tan's empire was shattered, as the psychic forces of the Immaterium were anathema to soulless entities whose existence was wholly contained within purely physical patterns of electromagnetic force. For all the destruction they could unleash, they were unable to stop the Old Ones and the younger races' relentless advance across the stars.
The C'tan, unified by this great threat for the first time in millions of years, sought a way to defeat the soul-fuelled energies of the younger species. They initiated a great warding, a plan to forever defeat the psychic sorceries of the Old Ones by sealing off the material universe from the Warp, a plan whose first fruits can still be found on the Imperial Fortress World of Cadia in the form of the great pylons that litter the surface of that world in intricate networks and create the area of space-time stability near the Eye of Terror known as the Cadian Gate. With their god-like powers, it was only a matter of time until the C'tan succeeded and the greatest work of the C'tan was begun. But before it was complete, the seeds of destruction the Old Ones had planted millennia before brought about an unforeseen cataclysm. The growing pains and collective psychic flaws of the younger races threw the untapped psychically reactive energies of the Immaterium into disorder. War, pain and destruction were mirrored in the bottomless depth of the sea of souls that was the Warp. The maelstroms of souls unleashed into the Immaterium by the carnage of the War in Heaven coalesced in the previously formless energies of the Warp. Older entities that had existed within the Immaterium transformed into terrifying psychic predators, tearing at the souls of vulnerable psykers as their own environment was torn apart and reforged into a realm of Chaos.
The Enslaver Plague
The denizens of the Warp clustered voraciously at the cracks between the Immaterium and the material universe, seeking new ways to enter the physical realm. The Old Ones brought forth new genetically-engineered warrior races to defend their last strongholds, including the technology-mimicking Jokaero and the formidable, green-skinned Krork who were the ancestors of the present day Orks, but it was already too late. The Old Ones' intergalactic Webway network was breached from the Immaterium and lost to them, several of their Warp Gates were destroyed by their own hands to prevent the entities of the Warp from spreading to uncorrupted worlds and Old Ones' greatest works and places of power were overrun by the horrors their own creations had unleashed. The most terrifying of these horrors were the Enslavers, Warp entities whose ability to dominate the minds of the Younger Races and create their own portals into the material realm using transmuted possessed psykers brought them forth in ever greater numbers. For the Old Ones, this was the final disaster as the Enslavers took control of their servants. The Pandora's Box unleashed by the creation of the Younger Races finally scattered the last of the Old Ones and broke their power over the galaxy once and for all. Life had stood at the edge of an apocalypse during the War in Heaven between the Old Ones and the C'tan. Now as the Enslavers breached the Immaterium in epidemic proportions, the survivors looked doomed.
The C'tan and Necrons Entombed
The Necrons had been vindicated in their pursuit only of science and control over the material realm and certainly took pleasure in seeing the Old Ones' civilisation collapse as a result of their over-indulgence of psychic power. Unfortunately, it seemed that the last of their own masters' food supply would be lost along with it. The C'tan, however, had a solution to even this as a result of their immortal perception of the passage of time. They would allow the Enslavers to take what was left of the sentient life in the galaxy and let it become an interstellar wasteland; the psyker swarm would then die away and in time the galaxy would evolve new lifeforms for the C'tan to consume. It would take millions of years, but what mattered is that they and their Necron servants would be there to take advantage of it.
The C'tan chose to escape the great catastrophe that was coming by descending into Necron stasis-tombs that would be sealed for tens of millions of Terran years. Their machine slaves and Necron warriors would guard them while they slept on Tomb Worlds purged of all life to keep the Enslavers from their door. Only when they were disturbed by a sentient species with the correct physical characteristics that would allow them to be both mastered and consumed as the Necrontyr had been would the Star Gods reemerge into the galaxy. This plan worked with an amazing degree of success until the Necrons were awakened by the forces of the Imperium of Man in the late 41st Millennium to plague the galaxy once more. By that time, only two of the C'tan emerged. They discovered a new and unexpected age of interstellar civilisation and war much like the one they left behind 65 million years ago. The galaxy is blossoming with life once more but is still overrun with latent psykers and worshippers of the infernal Chaotic Warp energies unleashed during the War in Heaven. It will take time and a great many machinations for the C'tan to regain their rightful places as the rulers of the galaxy; the agents of Chaos must be overthrown; the dangerous Eldar, inheritors of the Old Ones' mantle, eliminated; the great work cutting off the material universe from the Warp completed and Mankind subjugated before a new age of red harvests can truly begin. But the C'tan and the Necrons are ageless and undying, their technology is still unmatched by any of the Younger Races and time is always on their side...
The Age of Man
For millions of standard years after the Necrons and their C'tan masters went into hibernation on their Tomb Worlds, the devastated sentient populations of the galaxy slowly recovered from their "red harvests." In time, the Eldar emerged as the most dominant civilisation in the galaxy, with the core of their star-spanning empire located in the region of what would later become the Eye of Terror Warp rift. But on the planet called Earth and later Terra by its inhabitants, a humanoid species known as Mankind was rising to prominence over 40,000 standard years ago. During the Age of Terra, or the Age of Progress as it is sometimes called by Imperial historians, the human race advanced beyond its ancient pre-industrial past to obtain spacefaring capability and began to slowly settle the habitable worlds in its own solar system and in the star systems near its homeworld using massive sublight starships. During the next era of human history, the Dark Age of Technology, Mankind discovered how to manipulate the Warp to allow faster-than-light interstellar travel and psychic communications. With starships outfitted with Warp-Drives and human Navigators, Mankind began to rapidly expand beyond its home region of the galaxy, competing with the powerful Eldar empire for new worlds and resources. This period saw the development of the Standard Template Construct (STC) database of advanced technologies that were used to colonise the galaxy. Eventually humanity had settled on more than a million worlds, some habitable from the start for human life like Terra, others terraformed to make them livable. At its height in the Dark Age of Technology, humanity commanded technological prowess and scientific knowledge that has long been lost to the people of the present-day Imperium. In time, the scattered human worlds forged an interstellar federation to enhance their political and economic unity. This was a Golden Age for Mankind and this great civilisation persisted for long centuries.
But human scientists in their hubris created the true artificial intelligences later known in legend as the Men of Iron. Intended to serve humanity in both industry and war, the Men of Iron ultimately rebelled against the wishes of their human masters and unleashed a war across the galaxy to exterminate or enslave humanity that fragmentary ancient records indicate may actually have been even more destructive to human space than the Horus Heresy. The ancient human interstellar civilisation never recovered from the destruction of this conflict, though Mankind prevailed at great cost against its robotic children. Immediately after humanity had defeated the Men of Iron, the plague of uncontrolled psykers first appeared on human worlds. But Mankind was not yet ready for the burdens of psychic power and many of the newly emergent human psykers lacked the strength of will to control their powers. Many were possessed by Daemons and other Warp entities and proceeded to cause immense damage to their already battered homeworlds until psykers were often killed on sight as "witches" on many human planets.
But the true death knell of humanity's Golden Age was the coming Fall of the Eldar. As the Eldar empire reached its zenith in the 24th Millennium and its people lost themselves in orgies of hedonistic excess, their collective psychic emanations roiled the Warp and gestated a hideous new presence within the Immaterium, the Chaos God Slaanesh, the Prince of Pleasure. Slaanesh's growth so roiled the Aethyric dimension that it spurred on the human evolution towards becoming a fully psychic species like the Eldar, producing the plague of human psykers. At the same time, Slaanesh's gestation disrupted the eddies and tides of the Warp, leading to the emergence of massive Warp Storms across the galaxy. These storms cut off all interstellar travel and communications between the worlds of Mankind, which were so dependent on the Immaterium for both faster-than-light travel and astropathic communications. Plagued by psykers and unable to communicate or trade with the other worlds of its commonwealth, Mankind's great interstellar civilisation simply collapsed. Its planets were thrown into a terrible new era of technological decline, constant warfare, religious superstition, disease and death. Many of the human worlds of the galaxy were consumed by blood-letting and warfare as their economies collapsed with the end of interstellar trade and the lack of the goods that many populations had depended upon for survival. Whole worlds died as a new Dark Age claimed the whole of the human-settled galaxy, and so this time is remembered as the Age of Strife by Imperial historians. It lasted for almost 5,000 standard years of pain and terror.
When Slaanesh was at last born in the 29th Millennium, the psychic birth pangs of the new Chaos God echoed through the Immaterium and into the material universe, ripping open the massive rift between the realities now known as the Eye of Terror. This hideous Warp rift swallowed most of the homeworlds of the Eldar empire, destroying them, while the souls of billions of Eldar were swallowed by the bloated mass of psychic energy that was Slaanesh. Only those Eldar on the Craftworlds, the Maiden Worlds and within the labyrinthine corridors of the Webway were saved from the Prince of Pleasure's eternal hunger for Eldar souls. Yet the birth of Slaanesh also cleared the Warp of the continuous psychic emanations that had produced the constant Warp Storms in the material universe and had made interstellar travel and communications impossible.
On Terra, ravaged by millennia of competition and warfare between the tribes of techno-barbarians who had fought for control over the course of the Age of Strife, the future Emperor of Mankind finally ended his ancient habit of working anonymously over the millennia through a variety of different personas to better the human race. Realising that in its current straits humanity would never again be able to rise to its former greatness without the help he could provide, the Emperor revealed his full strength and power to the people of Terra and launched a great conflict known as the Unification War at the end of the 30th Millennium to unite all of Terra beneath his rule. Using advanced genetic engineering techniques to create an army of super-soldiers clad in Power Armour, the Emperor faced off against the techno-barbarians and defeated their armies one by one, forging them into a unified planetary government under his rule. With Terra united once more under an autocratic Imperial government, the Emperor next forged an alliance with the Mechanicus of Mars to provide him with the starships and technology he would need to reunite all the scattered worlds of Mankind into a single government under his own enlightened rule, a new Imperium of Man. The Emperor intended to spread civilisation and progress once more across the battered planets of humanity's realm now that the Age of Strife was ending and to replace the millennia of superstition and ignorance with the new cult of scientific rationalism and respect for human progress that he called the Imperial Truth. The Emperor hoped that the replacement of Mankind's old beliefs in magic and religion with the cold rationalism of science would strike a deep blow against the Ruinous Powers of Chaos and weaken their growing influence over both humanity and the galaxy at large.
To carry out his intentions, the Emperor needed military leaders of surpassing genius and physical might, men much like himself since he could not be in every place at once. From his own unique genetic material he created 20 genetically-engineered human males of unsurpassed beauty, size, strength and intellect, the Primarchs who would lead his armies of altered soldiers in conquest across the universe. But the Chaos Gods were not unaware of the Emperor's plans to strengthen the forces of Order across the galaxy and so they moved first, opening a Warp rift in the middle of the Emperor's own gene-lab beneath the Himalayan Mountains on Terra and teleporting the infant Primarchs, still in their gestation capsules, to various worlds across the galaxy. Unfortunately, many of them were tainted with the mark of Chaos in the process. Yet the Emperor was nothing if not resourceful. Using samples of genetic material that had been taken from the developing Primarchs, the Emperor created a new race of superhuman warriors, the 20 Legiones Astartes or Space Marine Legions, who would take the lead in the great expedition to reunify Mankind beneath the Aquila of the new Imperium. Dividing the Legions up into hundreds of different Expeditionary Fleets assisted by the forces of the Mechanicus of Mars, the Emperor initiated the Great Crusade to expand the Imperium of Man and spread its Imperial Truth across the galaxy.
In time, some 200 years after the start of the Great Crusade in the early 31st Millennium, the Imperium had spread its sheltering wings across hundreds of thousands of human worlds, restoring a measure of civilisation and progress to the scattered peoples of Mankind and inaugurating a new age in human history, the Age of the Imperium, our current era. In the course of the Great Crusade, the Emperor had rediscovered his scattered Primarch sons, and placed each of them in command of the Astartes Legion that had been created from their gene-seed. In particular, the Emperor placed his greatest trust in Horus, the mightiest and most gifted of all the Primarchs, the man in whose hands the Emperor ultimately entrusted the entirety of the Great Crusade when he returned to Terra to carry out his next project in pursuit of a new human Golden Age -- opening up the Webway for use by the Imperium.
But the taint of Chaos ran deep in some of the Primarchs. Horus, whose pride proved to be as large as his talents, was seduced to the side of Chaos through the machinations and lies of the Chaos Gods. Horus eventually convinced eight of his brother Primarchs and their Space Marine Legions to join him and turn Traitor to the Emperor. These Traitor Legions and their accompanying units of the Imperial Army and the Adeptus Mechanicus unleashed the horrendous interstellar civil war that is remembered only as the Horus Heresy. For seven standard years they made war upon the Loyalist forces, killing billions as they drove towards the heart of the Imperium in Horus' determination to overthrow his father and replace him as the Master of Mankind. In the end, the Traitor forces assaulted the great fortress of the Imperial Palace during the Battle of Terra, forcing the Emperor himself to take up arms to defeat his wayward son. On the bridge of Horus' battle-barge the Vengeful Spirit, the Emperor ended his son's life, and saved humanity from the unending nightmare of Chaos, but at a high price. The Emperor suffered a mortal wound and was placed within the Golden Throne, an ancient technological device of unknown origins that kept his ravaged body in stasis while still allowing his mind to roam free in the Warp, providing the psychic beacon of the Astronomican that tied the Imperium together while he combatted the whims of the Ruinous Powers. In time, the Imperial Truth was replaced by a new faith in the God-Emperor of Mankind; the religious superstition the Emperor had hoped to replace instead became the foundation of a far more effective shield against the ravages of Chaos vested in the simplest mantra of the new Imperial Creed: the Emperor protects.
In the 10,000 years since the end of the Horus Heresy, the Imperium has continued to expand across the galaxy. Despite the terrible threats presented by heretics, mutants, xenos and the Forces of Chaos, humanity has managed to remain the dominant species of the Milky Way Galaxy. Yet the political repression and outright acts of tyranny required to maintain human control over this vast domain have only worsened over the long centuries while human technological levels have continued to decline from what they were at the time of the Great Crusade. And now, in the last century of the 41st Millennium, the Imperium faces its greatest challenges. The Forces of Chaos, led by Horus' successor and former lieutenant, Abaddon the Despoiler, threaten to break through the cordon erected by Imperial forces over the fortress world of Cadia where they have been trapped since the end of the 13th Black Crusade. The Hive Fleets of the Tyranids are spreading like a plague of xenos locusts from the Eastern Fringes of the galaxy, intent on reaching the source of the Astronomican on Terra. Heresy and rebellion spread across the Imperium as never before. The Necrons and their C'tan masters, having slumbered for untold billions of years, are at last beginning to awaken across the galaxy, to begin harvesting anew. And now, in the halls of the Imperial Palace, new whispers have begun to gather, rumours which murmur that the Golden Throne has begun to fail and the Adeptus Mechanicus lacks the knowledge to repair it...
The Emperor Protect Us All.
- Warhammer 40,000: Rogue Trader (1st Edition)
- Warhammer 40,000 Rulebook (5th Edition)
- Codex: Necrons (3rd Edition)
- Horus Rising (Novel) by Dan Abnett
- Warhammer 40,000: Dark Heresy Core Rulebook (RPG)
- Battlefleet Gothic Rulebook
- White Dwarf 139, "Interstellar Travel"
- White Dwarf 140, "Interstellar Travel"