For a complete chronology of the events of the Imperium of Man visit Imperium of Man History.
The Age of the Imperium is the name given by Imperial lexographers and historitors to the period of human history that spans the 10,000 standard years following the end of the Horus Heresy and the emergence of the Imperium of Man in its recognizable form. The precursor to the Age of the Imperium began in the 30th Millennium when the Emperor of Mankind emerged from long centuries of obscurity to unify Terra beneath His rule and end the terrible suffering and civil conflicts of the Age of Strife. The Emperor forged a political and military alliance with the Cult Mechanicus that had reunified the Forge World of Mars and together the two most populous worlds of humanity birthed the Imperium of Man. Using the advanced technology of the ancient Mechanicum, the Emperor created the twenty Space Marine Legions of the First Founding to launch the "Great Crusade," an attempt to reunify all the human-settled colony worlds across the Milky Way Galaxy under a single government once more. While this campaign proved largely successful in reunifying the majority of the human race, that unity was eventually destroyed by the terrible galaxy-wide civil war known as the "Horus Heresy." Half of the Imperial armed forces, led by the Emperor's favoured son, the Warmaster Horus, were corrupted by the Dark Gods of Chaos and followed Horus into rebellion. The Traitor Legions and their allies launched themselves in an assault upon the Imperium that ultimately led to Horus' death, the Emperor's eternal internment within the Golden Throne and the dawn of a new age of technological stagnation and constant warfare. It is this terrible moment that truly marks the start of what became known as the Age of the Imperium.
Following the successful conclusion of the Unification Wars, the Emperor first ordered the construction of the great psychic beacon known as the Astronomican on Terra, which would enable His forces to expand the Great Crusade to the stars beyond the Sol System. Huge numbers of Tech-priests were brought from Mars to oversee the project and the majority of the Terran population were drafted to construct the towering machine-buildings needed to support this labour. At the time the Astronomican was the single largest artifice on Terra, and the entire device was merely a focus through which the Emperor could direct His fathomless psychic energies to generate a partly self-sustaining telepathic signal through the Empyrean (although few were aware of this fact at the time). The psychic navigational beam the Astronomican generated was able to propagate through the Warp and those attuned to its unique frequencies and modulations, the Navigators, were able to use it as a beacon and pole star when plotting journeys through the Immaterium. By this beacon the Warp could be travelled by human starships at speeds and with a margin of safety that had been unprecedented, although the risk, of course, could never be fully mitigated. The Astronomican was an incalculable boon to both the Great Crusade and the fledgling interstellar domain of Mankind that it was creating. In a similar way, the Emperor was able to shut down the Astronomican or interrupt the beam at will. Only a handful of individuals knew that the great signal was actually powered by the Emperor's psychic powers, and they lived in fear that should He be disabled or killed, the galaxy would be plunged into a new Age of Strife. Such was the Astronomican's effect that even in that distant age of the Imperium's first founding some referred to it as the Divine Light, or the Emperor's Light, often without fully realising the literal truth of those words. The sacred duty of powering the massive psychic beacon would eventually be shifted to a great choir of 10,000 Imperial Sanctioned Psykers after the Emperor was interred within the Golden Throne, heralding the birth of the Imperial Adepta that would become the Adeptus Astronomica.
During the era remembered as the Time of Rebirth the Imperium of Man slowly recovered from the Horus Heresy, economically, politically and even technologically. The myriad wars of the Great Scouring were fought in the years immediately after the end of the Horus Heresy and the death of the traitorous Warmaster.
In a lengthy campaign explored above, the Imperium's forces hunted and banished the remaining Traitor Legions from the occupation of human space. Eventually the Chaos Space Marines and the Ruinous Powers' other followers among the forces of Chaos found refuge in the massive Warp rift known as the Eye of Terror as the Emperor had planned. For a time the Imperium knew peace from the corrupted followers of the Chaos Gods.
At the same time, many alien races that had been fought during the Great Crusade reappeared in human space to take advantage of the disruptions caused by the Horus Heresy and plagued the vulnerable worlds of Man.
In 781.M31, Abaddon the Despoiler, the Chaos Lord of the Black Legion, made his first attempt to launch a new offensive against the Imperium of Man following the Horus Heresy. He initiated the campaign known as the 1st Black Crusade, which opened with the conflict remembered as the First Battle of Cadia. The 1st Black Crusade also marked the start of the Chaos Space Marines' ten-thousand-year-long attempt to throw down the Imperium that they named the "Long War." Abaddon had made many blood pacts with the Dark Gods in the wake of Horus' defeat during the Horus Heresy. Following this deadly incursion, the Ruinous Powers granted Abaddon the means to further increase his already formidable power. After the First Battle of Cadia was won, the forces of Chaos under Abaddon's command plunged the worlds of the Segmentum Obscurus into a terrible conflict that ravaged hundreds of worlds for several solar decades. At the end of that time, on the world of Uralan in the Eye of Terror, Abaddon recovered the Daemonsword Drach'nyen after battling his way through a haunted labyrinth to the great inner chamber where the blade had languished in stasis for millennia. The howling sword contained the bound essence of an ancient and dangerous Warp entity who had once been defeated by the Emperor Himself during the Horus heresy and had the power to rend reality apart wherever the weapon strikes. After the recovery of the malefic sword, Abaddon's power swelled to inhuman proportions much like his predecessor Horus, and he was recognised by the Chaos Gods as Horus Lupercal's true successor amongst the Traitor Legions, the new Warmaster of Chaos Undivided.
The Orks rampaged The Orks rampaged across the Imperium on a massive scale in 544.M32 during what became known as the War of the Beast. The number of greenskin attacks grew until it became the greatest Ork invasion that the galaxy had ever known to that time, eclipsing even the Ork WAAAGH! defeated by the Emperor and Horus during the Ullanor Crusade, which had earned Horus the title of Warmaster. Nothing was safe from the Orks' primal desire to conquer the galaxy and their widespread advances, including several assaults on Terra itself, were only halted when the Imperium resorted to the use of the most extreme measures, at great cost to the Chapters of the Adeptus Astartes. The Orks had developed six massive Warlords known as "The Beasts" by the Imperials, who each created six "Legions" of Orks similar to the ancient Space Marine Legions that had originally defeated them on Ullanor. These Orks were of a different sub-species than other Orks, were much more intelligent and could converse with humans fluently in their own language. They also developed gravitic and teleportation technologies more advanced than anything the Mechanicum had on hand, including the ability to teleport planets through what the Imperials named "subspace." The Orks built so-called "Attack Moons" by using gravitic technology to pull a planet's crust and mantle into space and then reshape it into a sphere. These Attack Moons were armed with "Gravity Whips" that could destroy entire fleets of battleships with crippling gravity waves. Three great battles were fought on Ullanor, the site of the ancient Ullanor Crusade and the capital of the new, advanced Ork civilisation and their greatest temple to the Ork gods Gork and Mork, to ultimately kill the Beasts using the aid of captured Ork psykers or "Weirdboyz" and the psychic null powers of the Sisters of Silence. The first of these battles was won by Vulkan, the Perpetual Primarch of the Salamanders Legion who aided the Imperium at this time and kept reincarnating after his death.
After the final conquest of the Beasts on Ullanor, the Mechanicus took over the world to strip away the Ork technologies in an attempt to learn how to teleport planets like Mars through the Warp and gain access to the Orks gravitic weapons. To keep the High Lords of Terra from knowing that they were violating Imperial doctrine to eschew any research into forbidden xenos technologies, the Tech-priests eventually teleported Ullanor into the Segmentum Solar, where it was wiped clean of Ork remains and reopened for human colonisation with a new name -- Armageddon. It is for this reason in the 41st Millennium that the Orks continually returned to claim the planet, never realising it is actually the home of their greatest empires of old. The War of the Beast brought many structural changes to the Imperium. The Inquisition was first divided into the Ordo Xenos and the Ordo Malleus at this time, and the Deathwatch, the Chamber Militant of the Ordo Xenos, was founded to face the Orks during the conflict. The position of Lord Commander of the Imperium, first among equals among the High Lords of Terra, was finally abolished and the Captain-General of the Adeptus Custodes was granted a seat on the High Lords' Senatorum Imperialis. In the wake of their near-destruction during the war, the Imperial Fists Chapter, long the sentinels of the Imperial Throneworld, left Terra behind, instead committing themselves to a never-ending Imperial Crusade against the foes of Mankind using their mobile fortress-monastery, Phalanx.
In 139.M41, the 12th Black Crusade, better known as the "Gothic War," was a vast campaign launched by Abaddon that engulfed the Gothic Sector of the Segmentum Obscurus after that sector was cut off from Imperial reinforcements and communications by a series of massive Warp Storms produced by the will of the Ruinous Powers. It consisted of hundreds of planetary invasions and naval battles spanning the time period 139.M41 - 160.M41 and only ended when Abaddon and his Chaos Space Marines, Renegade Chapters, daemonic hosts and rebellious Chaos Cults were forced to retreat into the Immaterium with the arrival of Imperial reinforcements as the Warp Storms that had provided cover for their invasion finally dissipated just as mysteriously as they had begun. On the Imperial side, dozens of Space Marine Chapters, nearly 100 Astra Militarum regiments and the better part of three Titan Legions took part, along with every naval vessel the Battlefleet Obscurus could muster. The conflict saw the destruction of several planets and four of the six irreplaceable ancient alien artefacts known as the Blackstone Fortresses as well as the deaths of millions, if not billions, of Imperial citizens. Most significantly, the events of the Gothic War revealed the true nature and purpose of the ancient spaceborne alien artefacts known to the Imperium as the Blackstone Fortresses, which had been created by the Old Ones to be used against the Necrons and were capable of destabilising stars and destroying entire solar systems. Most importantly, Abaddon and the forces of Chaos were able to escape back into the Eye of Terror with two of the Blackstone Fortresses, their future purpose unknown.
In 500.M41, in an event known as the Tears of the Emperor, the Imperium was swept by visions of the Emperor's tears. From backwards Feral Worlds to the most densely populated Hive Worlds, a million versions of the same story are told by holy men, street agitators, shamans, priests, and mystics. Primitives point to storm-filled skies, claiming that the drops falling from them are the tears of their mighty god. Upon Ecclesiarchy Cardinal Worlds, Arch-Deacons to lowly pilgrims claim to have seen statues of the divine Emperor shed tears. Chapter Masters and hive city urchins alike have visions of the Emperor stirring upon His throne, tears running from His empty sockets. Although the dreams take myriad forms, all know that the Emperor weeps not for Himself, but for the plight of Humanity.
As the threats to the Imperium grew in the last centuries of the 41st Millennium, Humanity stood on the precipice of utter extinction. The "Time of Ending" was the era of Humanity's judgement, where faith was tested by fire and every man or woman's courage was pushed to its limits -- and well beyond. By this time, secession, rebellion, Chaos corruption and heresy were now rife within every corner of the Imperium. Sensing weakness, alien empires ancient and new to humanity's experience -- Orks, Aeldari, T'au, Necrons and perhaps worst of all, the Tyranids -- closed in from every side. Zealots ranted that the xenos were Mankind's punishment, its just consequences for straying from the Emperor's guidance. The rise of mutants and witches was yet another sign of Humanity's sin. Desperate messages from across the galaxy echoed through the Warp. Astropaths worked feverishly to pull the transmissions from the Immaterium and translate them, to sift the meaning from the garble. The messages were increasingly dire: Planetary Governors sent desperate pleas for aid, Astra Militarum officers called for reinforcements, fleet commanders issued ominous warnings of enemy starship movements. The forces of the Imperium fought with the valour of ancient heroes, defending humanity from within, without and beyond -- but they could not be everywhere at once. The Space Marines and Astra Militarum were at war as never before, even during the Horus Heresy. The news grew worse daily, the attacks on the Imperium steadily increasing. Most ominous of all, the prescient foretold of great ripples in the Warp, like a swell in the water disturbed by some colossal but unseen menace in the depths below. Fell things were gathering in that dread realm, straining as never before to break the bounds of reality.
In 995.999.M41, Abaddon the Despoiler, the Warmaster of Chaos, launched the 13th Black Crusade out of the Eye of Terror with the intent to seize the world of Cadia and the surrounding worlds of the Cadian Gate it defends. This would allow the forces of Chaos to assault the heart of the Imperium for the first time since the Horus Heresy.
The forces of the Chaos Gods read like a roll call from epic battles of past ages. Always in the vanguard are the Black Legion, followed by the Death Guard, World Eaters, Alpha Legion, Thousand Sons, Night Lords and others from the annals of the Imperium's blackest days. Legions and Renegade Chapters of Space Marines long thought extinct renew their assaults on the realm of the hated Corpse Emperor.
Before them run infected, plague-ridden Chaos Cultists, deranged mutants and traitorous scum in numbers too great to be counted. Behind them tower Daemon Princes, Daemonhosts and other Warp creatures eager for the slaughter to be found in the mortal realm.
Astropaths everywhere cringe to open their minds to receive messages, for the Empyrean rings with mind-splitting peals, possibly the sound of the myriad tears ripping in the barrier between the Materium and the Warp, or perhaps it is simply the laughter of the Dark Gods.
The Imperium is forced to mobilise the largest military force in its history since the Heresy to meet the massive Chaos assault. After a gruelling campaign with a death toll that spirals into the trillions, Abaddon the Despoiler succeeds in tearing down the strange pylons that for millions of standard years had held the Cadian Gate as a stable region of space by using the damaged Blackstone Fortress Will of Eternity as an artificial meteorite to assault the Fortress World.
Despite the best efforts of the Imperium's staunchest defenders -- including the Black Templars, Imperial Fists, Dark Angels and Space Wolves -- the Fortress World of Cadia, lynchpin of the defences surrounding the Cadian Gate, eventually falls and a wave of Warp Storms roars into being across the length of the galaxy.
Though reinforcements continue to arrive for both sides, Imperial forces begin a great exodus while battles still rage throughout the sector.
Strange events, the appearance of the ancient Archmagos Dominus Belisarius Cawl and a cryptic alliance with a mysterious Aeldari religious faction known as the Ynnari conspire to awaken the Ultramarines Primarch Roboute Guilliman from his millennia-long slumber in a stasis chamber during the Ultramar Campaign of the 13th Black Crusade.
The Primarch is immediately embroiled in battle as a Chaos assault by the Black Legion as Abaddon attempts to prevent his return, though Guilliman successfully drives the servants of the Dark Gods from Ultramar, for a time.
Guilliman embarked upon the successful Terran Crusade through many tribulations to return to Terra and meet with his father the Emperor for the first time in ten thousand standard years. What passes between them is unknown, but when he emerges from the Imperial Palace, Guilliman initiates plans for Imperial survival, such as the creation of the Primaris Space Marines, that he first set into motion in the days immediately after the end of the Horus Heresy.
But even as Cadia falls and a Primarch returns to the Imperium, the Tyranids of Hive Fleet Leviathan march ever closer to Terra, drawn by the light and power of the Astronomican in the Warp inevitably towards the heart of the Imperium. The heroism of the Space Marines and the Inquisition manage to slow down the progression of the massive hive fleet, but its ultimate objective is never in doubt.
With doom looming over the Imperium, the Adeptus Mechanicus learned a terrifying secret in 986.999.M41: the mechanisms of the Golden Throne have begun to fail and they no longer possess the knowledge required to repair that ancient piece of technology. Unless something can be done, the God-Emperor will die and then humanity will face the coming darkness alone...
The Great Rift Opens. Soon after the fall of Cadia, reality tears itself apart from the Hadex Anomaly at the core of the Jericho Reach in the Eastern Fringe, to the furthest star system of the Segmentum Obscurus. From that hole come Warp Storms not seen since the Age of Strife, cutting off the galactic north from Terra and initiating a new historical era later named the "Era Indomitus." The initial period, known as the Noctis Aeterna -- or the Blackness -- is terrible indeed. For a time, all Warp travel is impossible and the far-spread planets of the Imperium are isolated, with no travel or astropathic communication between them. Worlds in their hundreds fall before the ensuing Chaos onslaught. The pulsing Cicatrix Maledictum spreads like an impenetrable curtain, robbing entire systems of the holy light of Terra. A chain reaction of Warp cataclysms rips across the Imperium, plunging its worlds into disaster and awakening the dormant powers of latent psykers across the galaxy. Countless civilisations are lost to daemonic incursions as the galaxy burns. To those on the Terran side of the rift, it is a tainted scar stretching across the sky. To those unfortunates on the far side, in the region now named the Imperium Nihilus, the "Dark Imperium," it is something much worse -- the very gates of Hell. No one fully understands the origins of the Great Rift, though there are many theories: the breach of the Cadian Gate during the Despoiler's recent 13th Black Crusade, the sorcery of the Daemon Primarch Magnus the Red during the Thousand Sons' invasion of the Fenris System, catastrophe in the Webway, the birth of Ynnead, the Aeldari God of the Dead, mass bloodshed and fire in the Damocles Gulf, the resurrection of the Primarch Roboute Guilliman -- all may have caused or contributed to it.
As the first Warp Storms broke over Holy Terra, its pollution-filled skies turned a roiling crimson. Khorne, heedless of the plans of his brothers and hungry to prove his superiority, sent forth eighty-eight cohorts of his daemon legions to assault the Imperial Palace. The Blood God wanted the glory of tearing down the Golden Throne for himself, and so the skies of Terra congealed into bloodclouds that deployed the Red Host directly before the Lion's Gate. The gun batteries of the Imperial Palace are second to none, yet they alone could not halt this red tide. Led by Roboute Guilliman, the newly reappointed Lord Commander of the Imperium, the Primaris Space Marines, Adeptus Custodes and Sisters of Silence fought side by side. Although the rash Chaos assault was turned back and broken long before it could reach the Eternity Gate to the Inner Palace, the High Lords of Terra were shaken at the boldness of the foe. Without the beam of the Astronomican, their arcane machinery and protective devices were not enough to halt the fell powers from materialising even on Holy Terra. Khorne, upon receiving the returning forms of his slain, grew so apoplectic in his rage that his fortress in the Realm of Chaos trembled. So great was the heat from his outburst that the essences of the eight Bloodthirsters that led the failed attack were wholly obliterated.
After his defence of Holy Terra, Roboute Guilliman gathered a new armada that he named the Indomitus Crusade, the largest concentration of Imperial military forces seen since the original Great Crusade over ten thousand standard years before. Along with elements of the Adeptus Custodes, a small contingent of the Silent Sisterhood, and a vast war host of Primaris Space Marines from many newly founded Chapters and the Legions of the Unnumbered Sons, the Primarch set a winding course. Strike forces from over a dozen pre-existing Chapters of Space Marines, led by the Imperial Fists, joined the fleet. Thus began many new legends as Guilliman travelled to aid beleaguered planets, breaking sieges and sweeping away Chaos and xenos invaders alike to bring hope back to the desperate defenders. It was not long before word began to spread, as all those planets that could still receive astropathic messages hailed the return of a hero out of myth. Once more, one of the demigods of the past fought for the Imperium of Man. The Indomitus Crusade would reach its end over a century into the 42nd Millennium at the Battle of Raukos. Afterwards, Guilliman would turn his attention to helping his Realm of Ultramar defeat the forces of the Death Guard Traitor Legion and the servants of Nurgle in the Plague Wars.
After sacrificing the Shieldworlds of the Cryptus System to fend off the xenos' earliest advance on the Baal System, the planet of Baal itself came under intense attack by Hive Fleet Leviathan. The Tyranid Hive Fleet was of such mass, even after its considerable losses, that it blotted the stars from the skies. Lord Commander Dante bolstered the formidable defences of the Blood Angels' homeworld and its moons like never before. Not one to await attack, he also sent forth scores of preemptive strike forces to delay, mislead, and whittle down the living armada. Hundreds of splinter fleets were thus defeated. Dante's call, beseeching the Blood Angels' Successors to send immediate aid to their parent Chapter, did not go unheeded. The Flesh Tearers were the first to arrive, and ultimately all the Successor Chapters save the Lamenters answered the call. Even the Knights of Blood, who had been declared Excommunicate Traitoris by the High Lords of Terra, arrived to bolster the defences. It was still not enough. Learning at an exponential rate, Hive Fleet Leviathan could not be thwarted by the same strategy twice. Advancing steadily, their superior numbers cleared the entire surrounding sector of life before the xenos made planetfall upon Baal and her twin moons. The first nineteen waves, each larger than the last, were driven off at great loss to the Blood Angels and their Successor allies. Five Chapter Masters fell in that bitter fighting, three in the Battle at the Dome of Angels alone. The Tyranids began the process of absorbing all biomass from Baal and its moons, absorbing even the radiation-poisoned deserts of Baal Secundus. With their defences in ruin and Baal's moons stripped and broken, the remaining Space Marines retreated back to the rubble of the Blood Angels' sprawling fortress-monastery. There, they prepared for a last stand as the next wave swept downwards. Doom, it seemed, had at last come to the Sons of Sanguinius.
It was then that the Great Rift cracked open the galaxy in the wake of the fall of Cadia to the 13th Black Crusade, and the withered Baal System was blasted by the aetheric storms. Although no further attack waves came from the Leviathan Hive Fleet, not a single Imperial defender remained alive upon the last moon, Baal Prime. On Baal itself there were already enough Tyranids there to destroy the Imperial troops many times over. Even with no chance of victory, Commander Dante led his troops, each fighting retreat seemingly more hopeless than the last. As the final perimeter was broken, the stars reappeared. Looking skywards, the Tyranids on the surface of Baal sought contact with their Hive Fleet, but it was gone, replaced by a newly arrived Imperial fleet. Like an angel of vengeance came Roboute Guilliman and his Indomitus Crusade. After many more battles, Baal was finally cleared of the xenos threat. A great rebuilding of both world and Chapter was undertaken, for the Blood Angels and their Successors were sorely needed elsewhere in the beleaguered Imperium. What became of the Leviathan is a mystery, although a clue was found upon the now-barren moon of Baal Prime. Xenos skulls were piled impossibly high in the much-reviled, eight-pillared symbol of one of the Blood Angels' most terrible and ancient nemeses: the Bloodthirster Ka'Bandha and his army of Khornate daemons.
The Plague Wars were an attempt by the daemonic and Heretic Astartes forces of the Chaos God Nurgle, including the Daemon Primarch Mortarion and his Death Guard Traitor Legion, to conquer the Realm of Ultramar and add it to the Plague God's growing realm in realspace. The Plague Wars began at some point after the birth of the Great Rift and the onset of the Noctis Aeterna and ended in ca. 111.M42, after the Primarch Roboute Guilliman successfully ended his Indomitus Crusade and brought Imperial reinforcements to defend Ultramar.
In a brief respite from the work of safeguarding the Emperor's realm after Mortarion's defeat, Guilliman ordered the rebuilding and decontamination of Ultramar, as well as the establishing of new procedures for creating further Ultramarines. It was not long before new Imperial Crusades called the Lord Commander of the Imperium away from Ultramar and back out into the dark galaxy. The Ultramarines then began the work of preparing their vengeance against the servants of the Dark Gods.
-Black Legion - A Codex: Chaos Space Marines Supplement (6th Edition) (Digital Edition), pp. 26-28, 31-40, 65, 70-71
-Codex Adeptus Astartes - Space Marines (8th Edition), pp. 16-17, 45
-Codex: Chaos Space Marines (3rd Edition, 2nd Codex), pg. 8
-Codex: Heretic Astartes - Chaos Space Marines (8th Edition), pg. 23
-Warhammer 40,000: Rulebook (8th Edition), pp. 40-47, 50-53, 123, 134, 152, 164-166
-Warhammer 40,000: Rulebook (6th Edition), pp. 168-177
-Imperium Nihilus - Vigilus Defiant (8th Edition), pp. 5-20
-Psychic Awakening: Faith & Fury (8th Edition), pp. 8-19
-Galaxy In Flames (Novel) by Ben Counter, pp. 280, 410
- Dark Imperium (Novel) by Guy Haley
-Devastation of Baal (Novel) by Guy Haley
-Warhammer 40,000 Timeline
-Gathering Storm - Part One - Fall of Cadia (7th Edition), pp. 12-13, 16, 20, 22-23, 26-33, 35-37, 40-42, 44, 48-49,52-53, 58-60, 62-65, 68-69, 72-78, 80-86, 88
-Gathering Storm - Part One - Fall of Cadia (7th Edition), pp. 12-13, 16, 20, 22-23, 26-33, 35-37, 40-42, 44, 48-49,52-53, 58-60, 62-65, 68-69, 72-78, 80-86, 88
-Gathering Storm - Part Three - Rise of the Primarch (7th Edition), pp. 4-93