The Warhammer 40k timeline spans roughly 65 million years, from the War in Heaven between the Old Ones and the Necrontyr to the current Indomitus Crusade in the 42nd millennium. The key events are the War in Heaven, the Fall of the Aeldari, the Age of Strife, the Emperor’s Unification Wars, the Great Crusade, the Horus Heresy, ten thousand years of the Age of Imperium, and the opening of the Great Rift.
This is the Warhammer 40k timeline stripped to its essential events — no deep dives, no tangents, just the major beats that shaped the galaxy. If you are new to the setting or simply want a reference you can scan quickly, this is your guide. One paragraph per era, covering sixty-five million years of galactic history.
What Happened During the War in Heaven?
The War in Heaven was the first great conflict in the galaxy, fought roughly sixty million years before the 41st millennium. The Old Ones — an ancient, psychically gifted species who could manipulate the Warp and had mastered the Webway — refused to share their secrets of immortality with the Necrontyr, a short-lived species ravaged by radiation from their dying sun. The Necrontyr, consumed by jealousy, went to war against the Old Ones. When they lost, they turned to the C’tan — star-eating entities of immense power — and made a terrible bargain. The C’tan transformed the Necrontyr into the Necrons — immortal metal bodies, but at the cost of their souls and free will. Together, the Necrons and C’tan shattered the Old Ones’ empire and broke the barriers between the Warp and realspace.
The war’s consequences were catastrophic and permanent. The Old Ones’ engineered servant races — the ancestors of the Orks and possibly the Aeldari — were scattered. The Warp, once a calm psychic dimension, became the roiling, daemon-infested hellscape it is in the current era. The Enslavers — Warp entities that possessed psykers and tore holes in reality — devastated what was left of galactic civilisation. After the war, the Necrons turned on their C’tan masters, shattering them into shards, and entered the Great Sleep — a hibernation that would last sixty million years. The galaxy was left in ruins, with the seeds of every future conflict already planted.
What Was the Rise and Fall of the Aeldari Empire?
After the War in Heaven, the Aeldari rose to become the galaxy’s dominant civilisation. Their empire lasted millions of years, during which they developed psychic abilities and technology that surpassed anything before or since. They were functionally immortal, their Webway network allowed instant travel between worlds, and they faced no serious threats. But their very success led to their downfall. With no challenges and no enemies, the Aeldari turned inward, pursuing ever more extreme sensations and experiences. A cult of excess and hedonism grew within their civilisation, feeding psychic energy into the Warp.
This psychic excess coalesced into a new entity — Slaanesh, the Chaos God of excess, perfection, and sensation. Slaanesh’s birth scream — the moment the new god achieved consciousness — was a psychic shockwave that annihilated the core of the Aeldari empire. Billions of Aeldari died instantly, their souls consumed by the newborn god. The psychic explosion tore a permanent hole in reality — the Eye of Terror — that would become the primary stronghold of the Chaos Gods in the material universe. The survivors scattered: some to the Craftworlds, some to Commorragh in the Webway (becoming the Drukhari), and some to Exodite worlds on the galaxy’s fringes. The Fall of the Aeldari is the defining tragedy of the 40k setting.
What Was the Age of Strife?
The Age of Strife — also called Old Night — was the period of human history that ran alongside the final decline of the Aeldari, ending with the Fall. The psychic turmoil of Slaanesh’s gestation generated massive Warp storms that made interstellar travel impossible; the god’s birth finally cleared them. Human colonies, which had spread across the galaxy during an earlier age of expansion, were cut off from each other and from Terra. Without faster-than-light travel or communication, the human diaspora fragmented into thousands of isolated civilisations, each facing its own threats.
The Age of Strife lasted approximately five thousand years and was characterised by total collapse. Human colonies were overrun by Orks, enslaved by other alien races, torn apart by internal conflict, or consumed by the emergence of uncontrolled psykers — humans whose psychic abilities manifested without training, often opening portals to the Warp and allowing daemonic incursions. Terra itself devolved into a post-apocalyptic wasteland ruled by feuding techno-barbarian warlords. It was the darkest period in human history — and it was into this darkness that the Emperor finally emerged.
What Were the Unification Wars and Great Crusade?
The Unification Wars were the Emperor’s campaign to unite Terra under a single government. Using his gene-crafted Thunder Warriors, the Emperor conquered the techno-barbarian warlords one by one, unifying humanity’s homeworld for the first time in millennia. He then replaced the Thunder Warriors with the Space Marines — more stable, more versatile, and designed for the long campaigns ahead. He created the twenty Primarchs, his demigod sons, and launched the Great Crusade — a two-hundred-year campaign to reunite every human world in the galaxy under the Imperium of Man.
The Great Crusade was humanity’s golden age. The Emperor and his Primarchs led the Space Marine Legions across the galaxy, liberating human worlds from alien overlords, establishing the Imperial Truth (a secular, rationalist philosophy), and building the infrastructure for a galaxy-spanning civilisation. Thousands of worlds were brought into compliance. The Imperium’s borders expanded faster than any civilisation in galactic history. For a brief, shining moment, it seemed as though humanity would fulfil the Emperor’s vision of a united, rational, secular empire that could stand against any threat — including the Chaos Gods.
What Happened During the Horus Heresy?
The Horus Heresy was the civil war that shattered the Emperor’s dream. Horus, the Emperor’s most favoured son and Warmaster of the Imperium, was corrupted by Chaos and turned half the Space Marine Legions against the Emperor. Nine Primarchs turned traitor, taking their Legions, along with vast portions of the Imperial Army, the Mechanicum, and the Titan Legions, into rebellion. The war lasted seven years and devastated the galaxy. Brother fought brother, worlds burned, and trillions died. The Heresy culminated in the Siege of Terra, where Horus’s forces besieged the Imperial Palace itself.
In the final confrontation, the Emperor faced Horus in single combat aboard Horus’s flagship. The Emperor killed Horus but was mortally wounded. His shattered body was placed on the Golden Throne — a psychic life-support machine that sustains him between life and death. From the Throne, the Emperor’s psychic power keeps the Astronomican lit (enabling interstellar navigation) and wards Terra against daemonic invasion. The traitor Legions retreated to the Eye of Terror, and the Imperium was left a scarred, diminished version of the Emperor’s original vision.
What Defined the Age of the Imperium?
The Age of the Imperium spans the ten thousand years between the Horus Heresy and the 41st millennium. It is a period of slow, grinding decay. The secular Imperial Truth was replaced by the Imperial Cult — a fanatical religion that worships the Emperor as a god. The Space Marine Legions were broken into smaller Chapters to prevent another Heresy. The Inquisition was founded to hunt heretics, aliens, and daemons. The Administratum grew into a bloated bureaucracy that could barely govern a fraction of the Imperium’s million worlds.
Throughout this period, the Imperium faced constant threats. Ork Waaaghs, Chaos incursions, Tyranid invasions, Necron awakenings, Drukhari raids, and internal rebellions consumed resources and lives in staggering quantities. The Imperium survived not through good governance but through sheer inertia and the willingness to sacrifice millions of lives for every strategic objective. Key events include the War of the Beast (the largest Ork invasion since the Heresy), the Age of Apostasy (a religious civil war), the Gothic War (Abaddon’s fleet campaign), and the multiple Black Crusades launched from the Eye of Terror.
What Is the 13th Black Crusade and the Great Rift?
The 13th Black Crusade was Abaddon the Despoiler’s ultimate gambit — the culmination of thirteen campaigns launched from the Eye of Terror over ten millennia. Unlike the previous twelve crusades, which had specific strategic objectives, the 13th Black Crusade was an all-out war of annihilation aimed at destroying the Cadian Gate — the primary fortified corridor between the Eye of Terror and the wider galaxy. Abaddon succeeded. Cadia, the fortress world that had held the line for ten thousand years, was destroyed. Its fall triggered the Great Rift — a galaxy-spanning tear in reality that split the Imperium in two.
The Great Rift — also called the Cicatrix Maledictum — runs from the Eye of Terror to the Eastern Fringe, dividing the galaxy into two halves. The northern half, Imperium Nihilus, is cut off from the Astronomican’s light, making Warp travel nearly impossible and leaving billions of Imperial citizens isolated and defenceless. The southern half retains some stability, but daemonic incursions along the Rift’s length are constant and devastating.
What Is the Indomitus Era?
In response to the crisis of the Great Rift, the Primarch Roboute Guilliman was resurrected from stasis by a coalition including the Mechanicus Archmagos Belisarius Cawl and the Aeldari Ynnari faction. Guilliman, the most administratively gifted of the Emperor’s sons, assumed command of the Imperium and launched the Indomitus Crusade — the largest military campaign since the Great Crusade, deploying the new Primaris Space Marines alongside conventional Imperial forces to stabilise the galaxy.
The Indomitus Crusade is the current era of Warhammer 40k. Guilliman’s forces have pushed back Chaos incursions, reinforced isolated Space Marine Chapters with Primaris Marines, and attempted to restore order to the shattered Imperium. But Guilliman faces challenges that would overwhelm even a Primarch — the Imperium’s institutional decay, the ongoing Tyranid invasion, the awakening Necrons, Ork Waaaghs of unprecedented scale, and the ever-present threat of Chaos from the Great Rift. The galaxy has never been in greater peril, and the Indomitus era is defined by a desperate race to prevent total collapse.
Frequently Asked Questions
How long does the entire 40k timeline span?
Approximately sixty-five million years, from the War in Heaven to the current Indomitus era in the 42nd millennium. However, most of the lore focuses on the period from the Great Crusade (circa M30) to the present (circa M42) — roughly twelve thousand years of human history.
Is the timeline set in the 41st or 42nd millennium?
The current era has crossed into the 42nd millennium. The Great Rift disrupted timekeeping across the galaxy, making precise dating difficult, but events after Guilliman’s resurrection are generally dated to the early 42nd millennium.
What is the most important event in the timeline?
The Horus Heresy is the defining event that shaped the current state of the galaxy. Without the Heresy, the Emperor would still rule, the Imperium would be secular and rational, and humanity might have achieved the Emperor’s original vision. Every tragedy of the 41st millennium traces back to Horus’s betrayal.
Will the timeline ever advance to the 50th millennium?
Games Workshop has historically been very slow to advance the timeline. The jump from late M41 to early M42 with the Gathering Storm and Indomitus Crusade was the largest timeline advancement in the game’s history. Future advances are possible but likely to be incremental rather than dramatic leaps forward.
Are the dates in the timeline exact?
No. The 40k universe uses a dating system that is deliberately imprecise, particularly for events before the Great Crusade. The War in Heaven happened “roughly sixty million years ago,” the Fall of the Aeldari happened at the end of M30, roughly ten thousand years before the 41st millennium, and even recent events are dated with caveats about unreliable records and Warp-time distortions. This imprecision is intentional and thematic.
What year is it in Warhammer 40k?
The current setting is the early 42nd millennium, roughly a century after the Great Rift opened at the very end of M41. Imperial dates are written like 999.M41 (the year 40,999), but Warp storms and the Rift make exact dating unreliable. Most sources therefore give only approximate years for current events.
How long before the 41st millennium was the Horus Heresy?
About ten thousand years. The Horus Heresy happened at the start of the 31st millennium and ended around 014.M31 with the Siege of Terra. That’s why the setting keeps saying the Emperor has sat on the Golden Throne for ten millennia. The Horus Heresy novels and tabletop game are set in that earlier era.
What does M41 mean in Warhammer 40k?
M41 means the 41st millennium, the years 40,001 to 41,000. Imperial dates put the year within the millennium first, so 999.M41 is the year 40,999 and 014.M31 is the year 30,014. Full Imperial dates can also include a check number and a fraction of the year, but fans usually quote just the year and millennium.