~125,000 BCE

Around 125,000 BCE, the Forerunners built the crown jewel of their civilization, an artificial world that served as the center of all Forerunner governance, Maethrillian.

~500 Mya

Sometime long before the time of the Forerunners, the Precursors created the Domain, a repository of all knowledge in the universe. The exact date is unknown, and while some sources say it was created 500 million years ago, others say it has existed for billions of years.

~15 Mya

Around fifteen million years ago, the Forerunner race was created by the Precursors in an effort to make a new species that could assume the Mantle of Responsibility.

~10 Mya

Ten million years ago, the Precursors, the species that populated the galaxy with intelligent life including Forerunners, determined the Forerunners were a failed experiment and decided to remove them from the Milky Way galaxy.

~107,445 BCE

The birth of the Flood is actually a series of events that can be traced to a time period around 10,000 years prior to the firing of the Halo Array in 97,445 BCE.

~107,445 BCE - 106,445 BCE

After the emergence of the Flood on ancient human worlds around 107,445 BCE, human civilization was desperate to expand their territory away from Flood-controlled regions of space. As part of this expansion, humans clashed with Forerunner-populated worlds, sparking a war between the two species.

~106,538 BCE

Sometime prior to the end of the Human-Forerunner Wars, ancient humans discovered a Precursor stasis chamber containing a creature they called the Primordial. The creature, along with the stasis chamber, was taken to Charum Hakkor where is was interrogated, teaching the humans on the origins of the Flood.

~106,498 BCE - 106,445 BCE

The Battle of Charum Hakkor was one of the final battles of the Human-Forerunner Wars and also one of the largest, spanning over fifty years and likely consuming millions of lives.

~98,445 BCE

After losing political power to the Master Builder and the entire Builder rate following the end of the Human-Forerunner Wars, the Didact placed himself in exile within a cryptum on Nomdagro, which was later moved to Erde-Tyrene.

~98,395 BCE

The end of the Human-Forerunner War, along with the political fight afterwards that led to the Exile of the Didact, spurred much debate within Forerunner leadership about the right course of action to defend civilization and the galaxy against the Flood, should they return.

~97,745 BCE

Around 97,745 BCE, nearly nine-thousand years since the Flood disappeared from the galaxy during the Human-Forerunner Wars and three-hundred years before the Great Purification, the Flood were first observed at the edges of the galaxy on the planet Seaward, a Forerunner colony world.

~97,745 BCE - 97,445 BCE

The Forerunner-Flood War was a military engagement between the Forerunner species and the Flood that took place over approximately three-hundred years from 97,745 BCE until 97,445 BCE.

~97,495 BCE

The release of the Primordial was an unintended consequence of the test-firing of a Senescent Halo, Installation 07, by the Master Builder and Mendicant Bias in the Charum Hakkor system during the Forerunner-Flood War, approximately fifty years prior to the end of the war and the Great Purification.

~97,455 BCE

Following the Didact’s self-imposed exile one thousand years prior after losing the political battle over the Forerunner defense plan against the Flood, the Didact is resurrected from his cryptum on Erde-Tyrene by Forerunner Manipular Bornstellar Makes Eternal Lasting, and humans Chakas and Riser.

~97,455 BCE

The Battle of Janjur Qom was a brief conflict between the San’shyuum and Forerunners on the quarantined San’shyuum homeworld of Janjur Qom several years prior to the firing of the Halo Array during the Great Purification in 97,445 BCE.

~97,455 BCE

After the Revival of the Didact and his exploration of the Charum Hakkor system with fellow Forerunner Bornstellar Makes Eternal Lasting and humans Riser and Chakas, the Didact and crew traveled to the quarantined San’shyuum homeworld of Janjur Qom to try and unlock more memories in their quest for understanding.

~97,454 BCE

The Fate of Maethrillian was a large-scale but brief battle between the Forerunners and the Halo Array under command of Mendicant Bias several years prior to the firing of the halos during the Great Purification in 97,445 BCE.

~97,454 BCE

In the aftermath of the Fate of Maethrillian and destruction of the Forerunner ecumene, Zeta Halo implemented it’s security measure designed to prevent the ring from falling into enemy hands and performed a slipspace jump into another system and put itself on a collision course with a nearby planet.

~97,450 BCE

After the Master Builder captured the Didact over Janjur Qom, he decided to dispose of the Didact on a derelict Forerunner ship with a handful of other political prisoners in an area of Flood-controlled space known as a Burn.

~97,445 BCE

The Battle of the Greater Ark was one of the final battles of the Forerunner-Flood War and saw the decimation of almost all remaining Forerunner forces just prior to the firing of the Halo Array during the Great Purification in 97,445 BCE.

~97,445 BCE

The behavior of the Ur-Didact following his encounter with a Gravemind and return to the Forerunner civilization became more erratic and harder for the IsoDidact and Librarian to cope with as the Forerunner-Flood War continued.

~97,445 BCE

The Great Purification was the final event of the Forerunner-Flood War, purging the entire Milky Way galaxy of all sentient life, including Forerunners, the Flood, and any other species that may have survived the Flood infestation.

~97,300 BCE

Over one-hundred years after the Great Purification, the few Forerunners remaining on the Lesser Ark became aware that the firing of the Halo Array may have had a detrimental effect on the Domain, and proceeded to the former Forerunner capital of Maethrillian to attempt to restore it.