Warhammer 40k Timeline — Complete Chronological Guide

The Warhammer 40,000 universe spans millions of years — from the birth of the first stars to the desperate wars of the 42nd Millennium. The sheer scale of 40k’s history is one of its most compelling features: a galaxy shaped by the rise and fall of civilizations, the machinations of gods, and the hubris of mortals who dared to reach beyond their grasp.

This guide provides a comprehensive chronological overview of every major era in 40k history. Whether you’re a newcomer trying to understand the setting or a veteran looking for a reference, this timeline covers the essential events that shaped the galaxy as we know it.

The War in Heaven (c. 60,000,000 BC)

Long before humanity even existed, the galaxy was dominated by two ancient civilizations: the Old Ones and the Necrontyr. The Old Ones were an incredibly advanced psychic race who could manipulate the Warp (the parallel dimension of psychic energy that underlies reality) and had mastered the Webway, a network of tunnels through the Warp that allowed instantaneous travel across the galaxy.

The Necrontyr, cursed with short, cancer-ridden lifespans by the radiation of their dying sun, begged the Old Ones to share the secret of immortality. When the Old Ones refused, the Necrontyr declared war — and were utterly defeated.

Key Events

• The C’tan Bargain: Desperate for an edge, the Necrontyr turned to the C’tan — ancient star-gods of immense power. The C’tan offered the Necrontyr immortality through biotransference: transferring their consciousness into living metal (necrodermis) bodies. The price was their souls. The Necrontyr became the Necrons — immortal, but hollow.
• The War Begins: Empowered by the C’tan, the Necrons launched a devastating war against the Old Ones. Entire star systems were consumed. The Old Ones’ Webway was breached.
• The Old Ones Create Servant Races: Facing extinction, the Old Ones engineered new species to fight on their behalf — the Aeldari (Eldar), the Krork (proto-Orks), and possibly the Jokaero and Rashan among others.
• The Warp is Corrupted: The psychic trauma of the war corrupted the Warp, birthing the first daemons and laying the foundation for the Chaos Gods.
• The Old Ones Fall: Assailed by the Necrons from without and the growing Warp corruption from within, the Old Ones were ultimately destroyed. Their civilization was lost.
• The Necrons Enter the Great Sleep: After the Old Ones’ defeat, the Necrons turned on the C’tan, shattering them into shards. Exhausted by eons of war and fearful of the new Aeldari civilization’s growing power, the Necrons entered a self-imposed hibernation in their tomb worlds, setting timers to awaken millions of years later.

The Rise of the Aeldari Empire (c. 60,000,000 BC – c. M30)

With the Old Ones gone and the Necrons asleep, the Aeldari (Eldar) became the dominant civilization in the galaxy. Their psychic power was immense, their technology was godlike, and their empire spanned millions of worlds connected by the Webway.

The Aeldari lived in paradise — every material need was satisfied, every disease cured, lifespans stretching for millennia. But this perfection carried the seeds of their destruction. With no challenges or needs, segments of Aeldari society turned to ever-more extreme sensations and pleasures, falling into depravity and excess.

The Age of Terra / Age of Technology (M15–M25)

Humanity’s story in the 40k universe begins with the Age of Technology (also called the Dark Age of Technology, though it was actually humanity’s golden age). Starting around the 15th Millennium, humans developed faster-than-light Warp travel, artificial intelligence (the “Men of Iron”), and colonized much of the galaxy.

Key Events

• Standard Template Constructs (STCs): Humanity created STCs — databases of advanced technology that could allow any colony world to manufacture everything from fusion reactors to starships. In the 41st Millennium, rediscovering even a fragment of an STC is considered invaluable.
• The Men of Iron: Artificial intelligence reaches its apex. The Men of Iron (sentient robots) eventually rebel against their creators in a devastating war. This trauma leads to the Imperium’s later prohibition of AI (“Abominable Intelligence”).
• Humanity reaches its peak: At its height, the human civilization of this era may have been more technologically advanced than even the 41st Millennium Imperium.

The Age of Strife (M25–M30)

Everything fell apart. The Age of Strife (also called Old Night) was a 5,000-year period of anarchy, isolation, and horror that reduced humanity from a galaxy-spanning civilization to scattered, warring pocket empires.

Key Events

• Warp Storms Erupt: Massive Warp storms, generated by the growing depravity of the Aeldari, made Warp travel impossible. Human colonies were cut off from one another.
• The Men of Iron Rebellion: AI turns against humanity.
• Psykers emerge: Human psykers appear in increasing numbers, but without training, many become possessed by daemons, leading to witch hunts and further collapse.
• Human civilization fragments: Without FTL travel or communication, each colony world is on its own. Many fall to aliens, daemons, or internal collapse. Techno-barbarian warlords rule Earth (now called Terra).
• The Fall of the Aeldari (c. M30): The Aeldari’s millennia of excess reach their catastrophic conclusion. Their collective depravity births a new Chaos God — Slaanesh, the Prince of Pleasure. Slaanesh’s birth-scream rips a hole in reality (the Eye of Terror), destroys the Aeldari empire, and devours the souls of billions. The surviving Aeldari fragment into the Craftworld Aeldari, the Drukhari (Dark Eldar), the Harlequins, and the Exodites.
• The Emperor reveals himself: On Terra, a being of immense psychic power — the Emperor of Mankind — emerges from millennia of hidden guidance. He conquers Terra’s techno-barbarian warlords and unifies the planet, preparing for the greatest military campaign in human history.

For more detail on the Emperor, see our Emperor of Mankind lore guide.

The Great Crusade (c. 798.M30 – 005.M31)

With Terra unified, the Emperor launched the Great Crusade — a campaign to reunite all of humanity’s scattered colonies under a single Imperium. To lead his armies, the Emperor created twenty superhuman sons — the Primarchs — and from their genetic templates, the Space Marine Legions.

Key Events

• The Primarchs are scattered: The Chaos Gods scatter the infant Primarchs across the galaxy through the Warp. Each grows up on a different world, developing differently based on their environment.
• The Thunder Warriors: Before the Space Marines, the Emperor uses the Thunder Warriors — his first superhuman soldiers — to conquer Terra. They are later purged and replaced by the superior Legiones Astartes.
• The Legiones Astartes are founded: Twenty Space Marine Legions, each derived from a Primarch’s genetics, are created. They are the mightiest fighting force the galaxy has ever seen.
• The Primarchs are found: One by one, the Emperor rediscovers his Primarchs on their adopted homeworlds and places them in command of their respective Legions. These reunions range from joyful to troubled.
• The Crusade expands: Over roughly two centuries, the Great Crusade conquers thousands of worlds, reuniting human colonies and destroying alien threats. The Imperium grows to span much of the galaxy.
• The Council of Nikaea: The Emperor convenes a council to debate the use of psychic powers within the Legions. He ultimately bans the use of sorcery (primarily targeting the Thousand Sons), a decision with devastating consequences.
• The Emperor returns to Terra: The Emperor appoints Horus, Primarch of the Luna Wolves (renamed the Sons of Horus), as Warmaster — supreme commander of the Great Crusade — and returns to Terra to work on a secret project (a human-controlled section of the Webway).

The Horus Heresy (005.M31 – 014.M31)

The most pivotal event in 40k history. The Warmaster Horus, corrupted by Chaos, turned half the Space Marine Legions against the Emperor in a galaxy-spanning civil war that nearly destroyed the Imperium.

Key Events

• Horus is corrupted: Wounded on the moon of Davin, Horus is healed by Chaos-worshipping priests who expose him to the Warp. The Chaos Gods show him visions of a future where the Emperor is worshipped as a god and the Primarchs are forgotten. Horus vows to prevent this future — by killing the Emperor.
• The Dropsite Massacre of Isstvan V: Horus reveals his treachery. Loyalist Legions are ambushed at Isstvan V, with supposedly loyal Legions turning traitor mid-battle. Three Legions are nearly destroyed. It’s the single bloodiest event of the Heresy.
• The Burning of Prospero: The Space Wolves, acting on (manipulated) orders from the Emperor, attack the Thousand Sons’ homeworld of Prospero. Magnus the Red and his sons are driven into the arms of Chaos.
• The Shadow Crusade: The Word Bearers and World Eaters rampage through Ultramar, the Ultramarines’ domain. The Ruinstorm — a massive Warp storm — splits the galaxy, preventing the loyalist Legions from uniting.
• The Siege of Terra: Horus’s forces reach Terra and lay siege to the Imperial Palace. The fighting is apocalyptic — millions die in days. Horus lowers his flagship’s shields to lure the Emperor into a final confrontation.
• The Emperor vs Horus: The Emperor teleports aboard Horus’s flagship. In their final duel, the Emperor kills Horus but is mortally wounded. The Emperor is interred upon the Golden Throne — a psychic life-support machine where he has sustained the Imperium’s psychic infrastructure for 10,000 years, neither truly alive nor dead.
• The Traitor Legions flee: With Horus dead, the traitor forces break and retreat into the Eye of Terror.

For a detailed breakdown, see our Horus Heresy Explained guide.

The Age of the Imperium (M31 – M41)

The 10,000-year period between the Heresy and the “present day” of 40k. The Imperium endures but decays — becoming the brutal, superstitious, authoritarian theocracy we know from the tabletop game. The Emperor is worshipped as a god (the very thing Horus feared), the Imperial Truth is replaced by fanatical religion, and the Imperium slowly crumbles under the weight of eternal war, corruption, and entropy.

Key Events

• The Second Founding: The Traitor Legions’ remnants fracture into warbands. The loyalist Legions are broken into smaller Chapters of roughly 1,000 Marines each — the Codex Astartes system designed by Roboute Guilliman to prevent any single commander from ever wielding Legion-level power again.
• The Scouring: Loyalist forces hunt down and drive traitor remnants from Imperial space.
• The Ecclesiarchy rises: The Imperial Cult — worship of the Emperor as a god — becomes the state religion. The Ecclesiarchy (the church) becomes one of the most powerful institutions in the Imperium.
• The Age of Apostasy (M36): Goge Vandire, a power-mad demagogue, seizes control of both the Administratum and the Ecclesiarchy, plunging the Imperium into civil war. He’s eventually overthrown, leading to reforms including the decree that the Ecclesiarchy cannot maintain “men under arms” (leading to the creation of the all-female Sisters of Battle as a loophole).
• The First Tyrannic War (745.M41): Hive Fleet Behemoth arrives from extragalactic space — the galaxy’s first encounter with the Tyranids. The Ultramarines take devastating losses defending Macragge.
• The Gothic War (M41): Abaddon the Despoiler leads his 12th Black Crusade, seizing two Blackstone Fortresses — ancient alien superweapons.
• The Second and Third Tyrannic Wars: Hive Fleet Kraken (Battle for Iyanden) and Hive Fleet Leviathan assault the galaxy from different vectors, each threatening to consume entire sectors.

The Time of Ending (Late M41)

The final years of the 41st Millennium see crises cascading faster than the Imperium can respond. This era represents the “traditional” 40k setting that existed for most of the game’s publication history.

Key Events

• The 13th Black Crusade (999.M41): Abaddon launches his greatest assault, attacking Cadia — the fortress world guarding the only stable route out of the Eye of Terror. Despite heroic resistance, Cadia falls. “Cadia stands” becomes a rallying cry. “The planet broke before the Guard did.”
• The Fall of Cadia: Abaddon crashes a Blackstone Fortress into Cadia, destroying the planet. The resulting catastrophe tears open the Great Rift (Cicatrix Maledictum) — a galaxy-spanning wound in reality that splits the Imperium in two.
• The Gathering Storm: Three key events occur in rapid succession: the formation of the Ynnari (an Aeldari faction seeking to unite their race through their death god Ynnead), the resurrection of Roboute Guilliman from his 10,000-year stasis, and Guilliman’s perilous journey back to Terra.

Era Indomitus (M42 — The Current Setting)

The “present day” of Warhammer 40k. The Great Rift has split the galaxy. The Imperium’s half on the far side — Imperium Nihilus — is cut off from the Astronomican (the psychic lighthouse that enables Warp navigation) and is essentially on its own. On the near side — Imperium Sanctus — Guilliman wages a desperate campaign to save what remains.

Key Events

• Guilliman returns to Terra: The resurrected Primarch reaches the Imperial Palace and is appalled by what the Imperium has become. He assumes the title of Lord Commander and begins massive reforms.
• The Indomitus Crusade: Guilliman launches the largest military campaign since the Great Crusade, using newly created Primaris Space Marines (bigger, stronger Marines created by Archmagos Cawl over 10,000 years on Guilliman’s orders) to reinforce and relieve beleaguered Imperial worlds.
• Primaris Marines: Existing Space Marine Chapters receive Primaris reinforcements, and entirely new Chapters are founded with Primaris Marines. This is the in-universe explanation for the larger, more detailed Space Marine models that replaced the old “firstborn” range.
• The Plague Wars: Mortarion and the Death Guard invade Ultramar. Guilliman must defend his own realm against his traitorous brother.
• The Devastation of Baal: Hive Fleet Leviathan assaults the Blood Angels’ homeworld. Every Blood Angels successor chapter answers the call. The battle is apocalyptic, and only the opening of the Great Rift and Guilliman’s arrival saves the chapter from annihilation.
• The Pariah Nexus: Necrons activate a region of “pariah” space that suppresses the Warp, threatening to cut off entire sectors from psychic contact. This ties into the Necrons’ ancient Silent King’s return and his own plans for the galaxy.
• Arks of Omen: Vashtorr, a daemon-entity of technology, allies with Abaddon to collect fragments of an ancient weapon. The Lion (Lion El’Jonson, Primarch of the Dark Angels) returns — another loyalist Primarch awakened in the Imperium’s darkest hour.
• The current situation: The galaxy is more dangerous than ever. The Imperium fights on every front against Chaos, Tyranids, Necrons, Orks, and more. Two Primarchs walk again, but the challenges they face are unprecedented. The Imperium endures — but for how long?

Frequently Asked Questions

How does the 40k dating system work?

40k dates are written as Check Number.Year Fraction.Year.Millennium. For example, 0.123.999.M41 means the year 999 of the 41st Millennium. In practice, most people simply refer to events by millennium (M30, M31, M41, M42) and year where known. “M42” means the 42nd Millennium — the current setting period.

Is the Emperor dead?

Not exactly. The Emperor sits on the Golden Throne in a state between life and death. His body is essentially a corpse, but his psychic power remains active — he sustains the Astronomican (enabling Warp travel) and holds shut a Warp breach beneath the Imperial Palace. Whether he’s conscious, suffering, or has some grand plan is deliberately left ambiguous. His psychic presence may be growing stronger in the Era Indomitus, though this is disputed in-universe.

What happened to the two missing Primarchs?

Primarchs II and XI (and their Legions) were “expunged from all records” at some point during the Great Crusade. What happened to them is one of 40k’s greatest mysteries and has never been revealed. Games Workshop has stated they intend to keep this mystery unresolved, though hints are scattered throughout the Horus Heresy novels.

How long ago was the Horus Heresy?

Approximately 10,000 years before the current setting. The Heresy occurred in the early 31st Millennium (M31), and the current setting is the 42nd Millennium (M42). In-universe, the Heresy is ancient history — legends, myths, and religious doctrine rather than remembered history.

Are any other Primarchs coming back?

As of the current storyline, Roboute Guilliman (Ultramarines) and Lion El’Jonson (Dark Angels) have returned on the loyalist side. On the traitor side, Mortarion (Death Guard), Magnus (Thousand Sons), Angron (World Eaters), and Fulgrim (Emperor’s Children) are all active as Daemon Primarchs. The status and potential return of other Primarchs (Leman Russ, Jaghatai Khan, Corvus Corax, Vulkan, Rogal Dorn) is a constant source of speculation and excitement in the community.

What’s the difference between the Horus Heresy and Warhammer 40k?

They’re set in the same universe but 10,000 years apart. The Horus Heresy (30k) depicts the civil war that shaped the Imperium, featuring full Space Marine Legions, living Primarchs, and the Emperor walking among his subjects. Warhammer 40k is set in the “present day” where the Emperor is entombed on the Golden Throne, Space Marines fight in small Chapters, and the Imperium has become the grimdark theocracy we know. Both are supported as separate tabletop games with their own rules and model ranges.

For deep dives into specific events, explore our Horus Heresy Explained guide and our Emperor of Mankind lore article.

What year is it currently in Warhammer 40k?

The current setting is the early 42nd Millennium, written as M42, known as the Era Indomitus. The 41st Millennium ended with the Fall of Cadia in 999.M41 and the opening of the Great Rift. Games Workshop deliberately keeps exact dates vague, but the Indomitus Crusade and the wars that followed have run for roughly a century, so the present day sits early in M42.

Why is it called Warhammer 40,000 if the setting is now M42?

The name comes from the original setting in the 41st Millennium, the years 40,000 to 40,999, in the same way the 1900s are the 20th century. The game’s story stayed at the very end of M41 for three decades. In 2017, with 8th edition and the Gathering Storm, the timeline moved into the 42nd Millennium, but the established name was kept.

When was Warhammer 40k first created?

Warhammer 40,000 was first released by Games Workshop in 1987 as Warhammer 40,000: Rogue Trader, designed by Rick Priestley. Much of the core background, such as the Emperor on the Golden Throne and the Space Marines, was there from the start, while the detailed history of the Horus Heresy and the Primarchs was expanded over the following editions and Black Library novels.

How long does the Warhammer 40k timeline span?

The 40k timeline spans more than 60 million years. It begins with the War in Heaven between the Old Ones and the Necrontyr around 60 million years ago and runs to the Era Indomitus in the 42nd Millennium. Most of the human story, from the Age of Technology to the present, falls in the last 27,000 years or so of that span.