Halo 4's billion year secret: The full Halo timeline

A complete timeline of the sci-fi series, and what it all means for Halo 4...

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  • The Forerunners learn of the Flood and begin planning construction of the Halo array as a 'Plan B' in case the Flood returns.
  • The Didact opposes construction of the Halo array and is sentenced to imprisonment on the newly-primitive Earth where his wife, the Librarian, makes her home.
  • Construction of twelve Halo rings begins, together with Shield Worlds intended to protect organic species from the Halos' devastating firing effect.
  • The Librarian begins archiving species from across the galaxy, placing samples of every species in sarcophagi on the Ark, far outside the Halos' effect.


  • Forerunners make first contact with the Flood on planet G617 g1. The investigating team are killed and the Flood escapes.
  • The Flood/Forerunner war begins. The Librarian hastens her work.


  • Forerunners create the Mendicant Bias AI to combat the Flood. It is placed in charge of Halo 07 and tasked with hunting the Flood Gravemind.
  • Halo 07 is test-fired, freeing the last surviving Precursor sealed away millennia earlier by Humanity. He is recaptured and imprisoned on Halo 07.
  • Mendicant Bias begins questioning the last Precursor on Halo 07. Their conversation lasts 43 years.

Halo: Cryptum


Since 343 took custody of the Haloverse they've published three novels tied directly to Halo 4. The first of the Forerunner Saga is Cryptum, telling the story of the Didact in 100,000 BC and establishing the complete history of the Forerunners and the original prehistoric human empire. It introduces the humans Chakas and Riser and sees the Forerunner Bornstellar become the new the Didact. The Didact eventually kills the man who imprisoned him, takes control of the Forerunner military, and heads off in search of his human friends Chakas and Riser, and the missing Halo 07.


  • The Didact is freed by the Forerunner Bornstellar after 1,000 years of imprisonment. They travel the galaxy together with the proto-humans Chakas and Riser. The Didact dies, but not before transferring his memories to Bornstellar who becomes the new the Didact. (Halo: Cryptum)
  • Manipulated by the last Precursor, Mendicant Bias returns on Halo 07 and turns on its creators, smashing the Forerunner capital. The new Didact takes control of the Forerunners' military.
  • Mendicant Bias seizes control of five of the twelve Halos. The Forerunners destroy them, leaving only seven.
  • Riser and Chakas journey to Halo 07 and help the Didact reclaimthe installation, restoring it to the Halo network. Chakas' mind is used as the template for 343 Guilty Spark. The last Precursor is revealed to be a Flood Gravemind and is killed by theDidact. (Halo:Primordium)
  • A Forerunner artefact bridging Earth and the Ark is buried in Africa by the Librarian.
  • Conversations between the Didact and the Librarian are recordedand stored on the Ark's Terminals (Halo 3).
  • Forerunners create the Offensive Bias AI to counter and fight Mendicant Bias.

Who is... The Librarian?


One of the Forerunner Lifeworkers, the Librarian relocated to Earth following the Human/Forerunner war and shepherded the devolved human species back towards civilisation. When her husband, the Didact, was imprisoned she placed a pre-programmed 'geas' in one group of humans, encouraging them over many generations to seek out the Didact's cryptum.

The two were briefly reunited on the Ark during the Flood/Forerunner war, but were separated when the Librarian continued her mission. In the final days of her life the Librarian constructed the artefact beyond Voi and forced Didact to activate the Halo array by preventing any possibility of her rescue. Somehow, she is still alive.

There is evidence in Halo Anniversary to suggest the entire Halo timeline is part of the Librarian's millennia-long plans. "Her strength was in planning and positioning the pieces, and then being bold enough to let it happen." says Guilty Spark in one of 343's Terminal videos. It took her 1,000 years to free the Didact and she did it without ever interfering directly. 100,000 years after her supposed death, other more secret plans are coming to fruition.

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