Warhammer 40k’s timeline is huge, but you only need a handful of eras to understand it. Here’s the shape of it without the homework.
The big picture in one breath
Humanity rises, falls, claws its way back, then nearly collapses again. That’s the whole arc.
The setting is dated in millennia, written as M41 or M42. The current ‘present’ sits around the 42nd millennium, right after a galaxy-splitting catastrophe.
The eras that actually matter
You’ll see dozens of era names thrown around, but most of them are footnotes. These are the ones worth knowing.
- Age of Terra (M1 to M15): baseline humanity spreads across the stars, no Emperor yet.
- Dark Age of Technology (M15 to M25): humanity’s golden peak. Incredible tech, and it doesn’t last.
- Age of Strife (M25 to M30): everything breaks. Warp storms, lost worlds, old night.
- The Fall and the Great Crusade (M30): the Eldar empire collapses and births Slaanesh, the Eye of Terror tears open, and the Emperor launches his Unification Wars and Great Crusade.
- The Horus Heresy (M31): the civil war that defines the entire setting. Half the Legions turn on the Emperor.
- Age of the Imperium (M31 to M41): ten thousand years of grinding decline, schism, and reform.
- The Great Rift and Indomitus Crusade (M41 to M42): the galaxy splits, and Roboute Guilliman returns to lead a counter-offensive.
Where the 41st millennium fits
Most classic 40k stories sit in late M41, the ‘Time of Ending’. It’s the era of the 13th Black Crusade and the fall of Cadia.
Then the Great Rift forms, and the timeline tips into M42. That’s where modern 40k lives, with the Indomitus Crusade pushing back against the darkness.
How the eras connect
Each disaster sets up the next. The Dark Age’s collapse creates the Age of Strife, which creates the Emperor’s rise, which creates the Heresy, which creates the Imperium you see today.
The Great Rift isn’t a random event either. It’s the payoff of ten thousand years of Chaos buildup, and it resets the status quo for the current edition.
| Era | Millennium | What happens |
|---|---|---|
| Age of Terra | M1 to M15 | Humanity spreads, no Emperor |
| Dark Age of Technology | M15 to M25 | Peak tech, then collapse |
| Age of Strife | M25 to M30 | Warp storms, isolation |
| Great Crusade | M30 | Emperor unites humanity |
| Horus Heresy | M31 | Civil war, Imperium shattered |
| Age of the Imperium | M31 to M41 | Long decline and dogma |
| Great Rift / Indomitus | M41 to M42 | Galaxy splits, Guilliman returns |
Key facts
- The timeline runs from M1 (Age of Terra) to M42 (the Indomitus Crusade).
- The Dark Age of Technology ends in M25, triggering the Age of Strife.
- The Fall of the Eldar and the birth of Slaanesh happen around M30.
- The Horus Heresy occurs in M31 and shapes the entire setting.
- The Great Rift forms in M41, splitting the galaxy and starting the current era.
FAQ
Do I need to know the whole timeline to enjoy 40k?
No. Most fans start with one faction or one novel and pick up the history as they go. The eras above are enough to orient yourself.
What’s the most important event in the timeline?
The Horus Heresy. It explains why the Imperium looks the way it does and why Chaos Space Marines exist at all.
When is ‘now’ in Warhammer 40k?
Roughly M42, after the Great Rift opened. Older stories are usually set in late M41.