A timeline of all major events in the Halo universe from the time of the Forerunners through the rule of the Created.
The Battle of Line Installation 1-4 was a conflict on Line Installation 1-4, a Forerunner defensive facility that was part of the Jat-Krula, the Forerunner's version of the Maginot Line during the Forerunner-Flood war in August 2552.
The Battle of Installation 04 was an engagement between the UNSC Pillar of Autumn and the Covenant Fleet of Particular Justice on and around the Forerunner megastructure known as Installation 04, or Alpha Halo, in the Soell system.
The Onyx Conflict was a major engagement between UNSC, Covenant, and Forerunner forces on and around the planet of Onyx in the Zeta Doradus system in October and November 2552.
The Battle of Installation 05 was an engagement between the Covenant forces, including those that fled the Battle for Earth, High Charity, and the Second Fleet of Homogeneous Clarity, and the UNSC-allied forces, including the UNSC In Amber Clad led by Miranda Keyes, and the Fleet of Retribution led by the Arbiter Thel 'Vadam.
The Battle of Installation 00 was a major conflict between the forces stationed aboard the UNSC Forward Unto Dawn and Arbiter Thel 'Vadam's Fleet of Retribution, and the Covenant fleet loyal to the Prophet of Truth.
Operation: JOVIAN WHISTLE was an operation executed by the UNSC 717th Xeno-Materials Exploitation Battalion to recover a Forerunner ancilla on the human colony world of Gao in the Cordoba system in the early summer 2553.
The Return to Installation 00 was an Office of Naval Intelligence mission undertaken by the UNSC Rubicon to return to the Ark following the Battle of Installation 00 and investigate the status of the facility in August 2554.
Operation: FAR STORM was a joint UNSC and Swords of Sanghelios mission to reactivate the Portal at Voi and travel back to Installation 00 after discovering the Halo array was counting down to activation in March 2555.
The Invasion of Earth was an attempt by the monitor of Installation 00 to harvest the Earth for resources to repair the Ark when the Portal at Voi was reopened in March of 2555.
Sometime in January 2557, Rion Forge, a post-war salvager, and her ship the Ace of Spades, discover the location of what was left of the Etran Harborage after the destruction of the shield world during the events of the Battle of the Etran Harborage in 2531.
The Battle of Requiem was a conflict between former Covenant forces under the command of Jul 'Mdama, UNSC forces from the UNSC Infinity and Forward unto Dawn, and Promethean forces under command of the Ur-Didact on Forerunner Shield World 0001, also known as Requiem, in July 2557.
The New Phoenix Incident was an attack by the Ur-Didact on the Earth city of New Phoenix on July 25th, 2557 using the Composer that he had acquired from Ivanoff Station the day prior.
The Mission to Installation 03 was a UNSC operation to investigate the loss of contact with a science outpost and Spartan-II Black Team on Gamma Halo immediately following the New Phoenix Incident in July 2557.
The Mission to Mount Kilimanjaro was a trek undertaken by 343 Guilty Spark, Rion Forge, and the crew of the Ace of Spades to find the Librarian and, in the case of Spark, gain access to the Domain in September 2557.
Operation: ATHENA was a covert UNSC mission to infiltrate the Song of Retribution, and retrieve the Janus Key from Jul 'Mdama and his Covenant remnant forces in September 2558.
The Raising of the Guardians was a series of events involving the awakening and unearthing of Forerunner ships known as Guardians by Cortana in late October 2558.
~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.
~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 - 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.
~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 - 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.
~97,455 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.
~97,454 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.
~97,445 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 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.
