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.
~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.
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.
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.
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.
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.
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.
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.
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.
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.
Birth of an EmpireMost of the history of the Forerunners is shrouded in mystery. What is known is the entire Forerunner species, like most species in the Milky Way, were created by the Precursors millions of years ago. When the Forerunners became too powerful and arrogant, the Precursors deemed them unfit to protect the Mantle, and decided to eradicate the galaxy of them to give ancient humanity their turn at earning the right to be defenders of the Mantle. When the Forerunners learned of this plan, they went to war, defeating and wiping out all Precursors from the Milky Way and Large Magellanic Cloud nearby, who were too shocked to fight back. This war shamed the Forerunners, who erased it from their history, not even allowing those who fought to return to Forerunner society. The Forerunners continued their dominance over the galaxy for the next ten-million years, growing and expanding their reach to include over three-million worlds within the galaxy.
Although the Precursors were wiped out by the Forerunners, their legacy lingered. Some Precursors avoided complete death by converting themselves into a desiccated powder and sending it via ships to the edges of the Milky Way. At least one other was mutated and locked away on an asteroid in the depths of space, biding their time until they were found.
Their time came when ancient humanity stumbled upon the powder, feeding it to their pets and through continued mutation, created the Flood. The threat the Flood posed to humanity forced them to expand their territory as worlds were lost, bringing them into contact with the Forerunners and sparking the Human-Forerunner Wars. Fighting both the Flood and the Forerunners was too much for them to manage, and it almost consumed them completely, until the discovery of the Primordial on a rock in deep space, who unbeknownst to humanity, took command of the Flood and sent all of them out of the galaxy. This nearly allowed humanity to survive against the Forerunner threat, but a betrayal by their allies the San’Shyuum tilted the war in the Forerunner’s favor permanently.
Having won the war against humanity, the Forerunners allowed some humans to survive, though they were devolved as punishment and to not pose a continued threat to the Forerunner empire. Meanwhile, the Didact, commander of the Forerunner military, tried using his hard-won political capital to support his plan for building hundreds of shield worlds across the galaxy, should the Flood return. He was successful for a while, but eventually the Master Builder convinced the Forerunner ecumene that his plan for building a intra-system defense platform known as the Halo Array, which was later redesigned to become a galactic weapon of last resort against the Flood. To avoid political retaliation on himself and all Warrior-Servants from the Master Builder and the entire Builder rate, the Didact placed himself into exile, spending the next thousand years isolated from the galaxy in a cryptum.
Fight For Survival
Inevitably, the Forerunner’s worst fear, that the Flood would return, came to pass. They rapidly began taking entire solar systems from the Forerunners, and within two-hundred years had made huge in-roads in the Milky Way. The Forerunner’s situation was made significantly worse when, during a test-firing of the Master Builder’s new Halo Array, the Primordial was released from his time-lock on Charum Hakkor, eventually convincing the Forerunner AI Mendicant Bias to fight for the Flood and commandeering one of the halo installations. Through the workings of the Librarian, the Didact was finally revived from his exile, though he would quickly be captured by the Master Builder and left for dead.
The Master Builder’s actions with the Didact and during his ruthless attack on Janjur Qom finally crossed a line with the Forerunner government, however, and with the threat of the Flood more immediate than ever, the Master Builder was put on trial on Maethrillian for his crimes against the Mantle. This trial barely had a chance to get started, though, as Mendicant Bias, along with the Primordial and the stolen halo, arrived at Maethrillian, sparking a violent battle that left the entire Forerunner capital devastated.
Pushed back onto their heels, the remaining Forerunners fought valiantly against the Flood, spending the next several years trying to keep the Flood from making further advances into Forerunner territory, but to no avail. Eventually the Forerunners lost the entire galaxy, with the remaining forces all converging at the Greater Ark, where they made a heroic last stand, though even with one large fleet and a halo remaining, the Forerunner forces were quickly overrun and the Greater Ark was destroyed. Only a select few managed to escape the battle before becoming completely overwhelmed, running to the Lesser Ark, the forge for the Neoteric Halo Array and galaxy-spanning weapon of last resort. Here, the IsoDidact initiated the Great Purification, eliminating all sentient life from the entire Milky Way and clearing out all traces of the Flood from the galaxy.