Editing Forerunner-Flood war

{{Status|Canon}}{{Status|Featured}}
{{Battle infobox
|prev=[[Human-Forerunner wars]]
|conc=
|next=*[[War of Wills]]
*[[Clan Battles of Sanghelios]]
|image=[[File:Old HW EarlyEfforts.jpg|300px]]
|conflict=
|date=[[97,764 BCE]] - [[97,445 BCE]]{{Ref/Book|Id=enc22pg9|Enc22|Page=9}}
|place=[[Milky Way]]
|result='''Pyrrhic Forerunner victory'''
*[[Halo Array]] [[Great Purification|sterilizes the galaxy]]
*Near extinction of the Forerunners and end of the Forerunner [[ecumene]]
|side1={{Icon|Forerunner}} [[Ecumene|Forerunner ecumene]]
|side2={{Icon|Flood}} [[Flood]]
|commanders1=
*[[Ur-Didact]]
*[[IsoDidact]]
*[[Librarian]]† 
*[[Master Builder]] [[Faber]]† 
*[[Mendicant Bias]] (before defection)
*[[Offensive Bias]] (constructed late in the war)
|commanders2=
*[[The Primordial]]†
*[[Gravemind]]†
*Mendicant Bias (after defection)
|forces1=
Forerunner military
*Trillions of [[Warrior-Servant]]s<ref>[https://www.halowaypoint.com/en-us/news/canon-fodder-uncharted-waters '''Halo Waypoint''': ''Canon Fodder - Uncharted Waters'']</ref>
*[[Builder Security]]
*[[Forerunner fleet]]
*3 million+ Forerunner planets
*Numerous Installations
**Many planetary navies
**[[Emergency Circumstance Fleet]]
**[[Security Fleet]]
**[[Suppression Fleet]] 
**[[Primary Pioneer Group]]
**[[Advance Survey Team-Alpha]]
*Numerous [[Sentinel]]s
|forces2=
*Trillions of Flood
*Millions of captured unarmed superluminal vessels
*Thousands of captured warships
*Numerous [[star road]]s and other Precursor constructs
|casual1= Near total: Most are killed by the activation of [[Halo Array]] while few survive and depart the galaxy.
|casual2= Extremely heavy: All Flood and Flood biomass is destroyed except for those contained in secure Forerunner facilities; all Precursor constructs destroyed
}}
{{Quote|A hundred thousand years ago, a [[Ecumene|great civilization]] existed in this universe. Like all great civilizations, they faced a sudden and dire turn of events. A threat to their primacy from ''outside''. Something they never expected, never prepared for... a deeply alien threat they called simply the [[Flood]].|[[Cortana]]<ref name="origins">'''[[Halo Legends]]''' - ''[[Origins]]''</ref>}}

The '''Forerunner-Flood war''', known as the '''Flood war''',{{Ref/Reuse|Id=enc22pg9}}{{Ref/Book|Id=enc22pg282|Enc22|Page=282-283}} was a pivotal galactic conflict that occurred between the [[Forerunner]]s and the [[Flood]] parasite. It was started on [[Seaward|G617 g1]] around [[97,745 BCE]] and lasted approximately three centuries. The Forerunners concluded the war in [[97,445 BCE]] with the creation and activation of the [[Halo Array]], seven superweapons that [[Great Purification|purged the galaxy]] of all [[Sentience|sentient]] life in order to stop the Flood. The conflict ended the Forerunners' eons-long rule in the galaxy; most of their [[ecumene]] having fallen to the Flood, the few remaining members of the species went into exile after completing the [[Reintroduction|repopulation]] of the galaxy's sentient species from specimens [[Conservation Measure|preserved]] at [[Installation 00|the Ark]].

==Background==
[[File:Crowd of Forerunner.jpg|thumb|250px|left|Forerunners gathered in an assembly.]]
The [[Forerunner]]s were an ancient race who thrived as the dominant civilization in the [[Milky Way]] galaxy, organizing their [[ecumene]] over millions of terrestrial planets. They derived their authority from the [[Mantle]], their pledge to watch over and preserve all life in the galaxy. The Forerunners' society was based on caste-like strata known as [[rate]]s, with a [[Warrior-Servant|dedicated military class]] which included both naval elements and ground forces. Their technological capacity was without equal, in areas such as the understanding of [[Slipstream space|slipspace]], energy manipulation, [[artificial intelligence]] and [[astroengineering]]. They measured technological advancement in a [[Technological Achievement Tiers|succession of Tiers]].<ref name="bestiarum">'''[[Bestiarum]]'''</ref>

While powerful, the Forerunners were not the only major civilization in the galaxy. Other races with interstellar empires included [[Ancient humanity|prehistoric humanity]], who had [[Human-San'Shyuum alliance|allied]] with the early [[San'Shyuum]]. Around [[107,445 BCE]], the [[Flood]] emerged as a threat within the humans' territory, supposedly having entered the galaxy from [[Path Kethona|one]] of the [[Magellanic Clouds]]. The infection caught the humans and San'Shyuum by surprise, infecting their populations and taking their worlds at a steady rate. At a certain point during the conflict, however, the Flood stopped infecting humans altogether and began to recede from the galaxy. Although widely believed to be the result of a cure created by humanity,<ref>'''Halo: Silentium''', ''page 37''</ref> this retreat was in fact due to the Flood's own long-term strategy to bring ruin to the Forerunners.<ref>'''Halo: Primordium''', ''page 364''</ref>

Unknown to the Forerunners at this time, the Flood was actually a manifestation of the [[Precursor]]s, a race of incredibly powerful beings who seeded the galaxy with life. Ten million years earlier, the Forerunners had [[Forerunner-Precursor war|rebelled against the Precursors]] and driven them to extinction; those who survived transmuted themselves to a molecular powder, meant to regenerate the Precursors at a later time. When biological beings came into contact with this powder—corrupted over millions of years—it manifested itself as a parasitic lifeform; the earliest stage of the Flood. Far from accepting defeat and extinction, the Precursors decided to wield their new form as an instrument to exact their revenge on the Forerunners for their crimes, and to bring unity to all life.<ref name="s173">'''Halo: Silentium''', ''pages 173-175''</ref>

The Forerunners first encountered the Flood during this conflict, witnessing its frightening power firsthand. Even at its withering state, the Flood proved to be a potent threat, infesting hundreds of [[Forerunner fleet]]s before the [[Warrior-Servant|Warriors]] adopted a policy of total extermination, destroying all traces of the Flood wherever they were found.<ref>'''Halo: Silentium''', ''page 36''</ref> Combined with the humans and San'Shyuum practicing a similar strategy for several centuries, no trace of the Flood seemingly remained in the galaxy afterward.<ref name="c34">'''Halo: Cryptum''', "Chapter 34"</ref>

While quelled for a time, the threat of the Flood would shape Forerunner politics for millennia to come. Two major factions emerged in the Forerunner political scene with differing views on how to best prepare against the parasite's return. A series of devastating superweapons, known as [[Halo Array|Halos]], was created by the [[Builder]]s while the [[Promethean]]s, led by the [[Ur-Didact|Didact]], devised a more strategic defense solution consisting of numerous military installations known as [[Shield World]]s. However, the Prometheans eventually lost to the Builders and were forced into exile, securing [[Master Builder]] [[Faber]]'s position in the [[Ecumene Council]]'s favor for over a thousand years. This infighting eroded the Forerunners from within, making them more vulnerable against the Flood's second wave.{{Ref/Reuse|c34}}

Aware of the inevitability of the return of the Flood threat, the [[Lifeworker]]s led by the [[Librarian]] began indexing and protecting species across the galaxy. The Halos and their extragalactic construction facilities—[[Ark]]s—were constructed with this [[Conservation Measure]] in mind, designed to house artificial ecosystems and countless sentient species, a means to partially undo the damage on galactic life in the event the Halos were used.{{Ref/Reuse|c34}} Due to its colossal scale, this indexing and preservation project would last all the way until the end of the conflict with the Flood, and even then failed to save even remotely all of the galaxy's sentient life.<ref name="s27">'''Halo: Silentium''', ''page 27''</ref>

After over nine thousand years, the Flood returned, contesting the Forerunners for control of the entire galaxy. While the Flood sought to assimilate all sentient life, the Forerunners attempted to defend against the Flood threat using several measures to both directly combat them as well as carry out research in regards to the parasite's capabilities.{{Ref/Reuse|origins}}

==War==
===Beginning===
{{Quote|It devoured everything it touched. At first, their technology, their courage seemed like it might prevail. But they waited too long to see the threat, to join the fight. The Flood had spread too far and too wide.|Cortana on the Forerunner-Flood war.}}
[[File:H4 - Warrior-Servants 2.jpg|thumb|300px|Forerunner Warriors stand ready against the Flood.]]
After nearly ten thousand years of absence, the Flood reappeared on the planet [[Seaward|G617 g1]], a lightly inhabited world harboring a small commune of Forerunners. The Flood initially caught the Forerunner military by surprise, using captured non-military vessels to penetrate local Forerunner naval blockades to descend and land upon Forerunner-colonized worlds, overrunning local defenses and converting billions of Forerunners per world with hundreds of millions of Flood forms. Eventually, Forerunner fleets were forced to commence [[orbital bombardment]] on Flood-infested worlds to prevent the Flood's spread to other planets.<ref name="h3terminals">'''Halo 3''', ''[[Terminal (Halo 3)|Terminals]]''</ref>

===Stalemate===
{{Quote|Know that a thousand other plans were tried and failed. Millions of brave and honored souls died trying to avert this terrible, desperate situation.|A Forerunner log describing the situation the Forerunners found themselves in.<ref name="iris1">''[[Iris]]'', Episode 1: [[The Unknown Helper]]</ref>}}
[[File:Ships fr.png|thumb|left|300px|Forerunner ships combining their firepower for an [[orbital bombardment]].]]
As the Flood grew in number and became more intelligent in the process, the Forerunners identified a centralized intelligence coordinating their efforts: the [[Gravemind]], the consciousness of the Flood itself, embodied in agglomerated collectives of biomass and in the millions of Flood forms.{{Ref/Reuse|bestiarum}} Using attrition tactics, the Flood gradually weakened the most formidable Forerunner naval countermeasures, one of which consisted of using [[Keyship]]s and drawing the Flood into pricey naval engagements. However, even Forerunner commanders realized that their naval tactics were being overcome, and a new solution was necessary if the Forerunners were to pull of out this stalemate.{{Ref/Reuse|h3terminals}}

The highest levels and tiers of the [[Forerunner Fleet Command]] began to realize that Forerunner species' extinction was plausible at the Flood's discretion as so many Forerunners had fallen victim to the Flood. As the Flood continued to spread, planetary self-bombardment after Flood infestation turned into complete system-wide destruction by detonating planetary system stars after a large Flood presence was detected in a Forerunner system. Forerunner military forces were ordered to don [[Combat skin|heavy armor]] and other personnel were ordered into protective stasis.{{Ref/Reuse|h3terminals}} Flood were taken into [[M-series facility|M-type installations]] and studied in an effort to find yet another countermeasure.{{Ref/Reuse|bestiarum}}

Hundreds of other unsuccessful methods were attempted by the Forerunners to overcome the Flood.{{Ref/Reuse|iris1}} Among these failed plans was the use of the [[Composer]], a machine designed to circumvent Flood infection by [[Mind transfer|translating]] an organic being's mental pattern into data and then transferring that pattern over an artificial body devoid of Flood infection. Unfortunately, this process proved to be flawed—all infected Forerunners treated with the Composer succumbed to decay and gruesome death.<ref>'''Halo: Silentium''', ''page 40''</ref> While galaxy-wide sterilization using the Halo rings existed as an option, the Forerunners would not resort to the Halos until the very end, viewing them as contrary to their [[Mantle]] to protect life.

On a larger scale, the Forerunners were relatively successful in keeping the Flood threat contained during the initial stalemate, lasting nearly three hundred years: no more than twelve outer systems were lost over this period.<ref name="c244">'''Halo: Cryptum''', ''page 244''</ref> For a significant amount of time, the Forerunner government managed to suppress information on the Flood threat, keeping its true nature hidden from the general populace of their core systems to avoid panic; the Flood was publicly claimed to be a mutation-inducing disease caused by stellar radiation.<ref name="c235">'''Halo: Cryptum''', ''page 235''</ref> However, during the stalemate, the Flood was secretly readying for an attack.{{Ref/Reuse|h3terminals}}
{{Clear}}
===Crisis===
{{Quote|I kill you all and I enjoy it. I destroy you in your indolent billions—in your gluttony, in your self-righteousness, in your arrogance. I pound your cities into dust; turn back the clock on your civilization's progress. What has taken you millennia to achieve I erase in seconds. Welcome back to the [Stone Age], vermin. Welcome home.|An excerpt of Mendicant Bias' hate-fueled diatribe against the Forerunners after the AI's defection to the Flood.{{Ref/Reuse|h3terminals}}}}
[[File:Mendicant.jpg|thumb|300px|A now rampant [[Mendicant Bias]] defects to the Flood.]]
The Forerunners had created a powerful [[Contender-class artificial intelligence|''Contender''-class artificial intelligence]] known as [[Mendicant Bias]], and tasked it with leading all of their defensive efforts. Mendicant had deployed major fragments of itself on numerous warships as well as all of the twelve installations of the original Halo Array. Around [[97,495 BCE]], Mendicant Bias was charged with the first test-firing of a Halo, [[Installation 07]], near the former [[Precursor]] world of [[Charum Hakkor]]. As a result of this small-scale activation, an ancient entity imprisoned on Charum Hakkor, known as the [[Primordial]], was released and subsequently transported to Installation 07 for study. [[Master Builder]] [[Faber]] tasked Mendicant Bias with interrogating the Primordial before having Installation 07 moved to a hidden locale to conduct his own unsanctioned experiments in secret.<ref>'''Halo: Cryptum''', "Chapter 39"</ref> During its 43-year long discourse with the Primordial, Mendicant Bias was convinced by the entity, actually a [[Gravemind]], to turn against its Forerunner masters.<ref name="p272">'''Halo: Primordium''', ''page 272''</ref>

Around the same time, Faber used Installation 07 to suppress a [[San'Shyuum]] [[Battle of Janjur Qom|insurrection]], practically wiping out the species aside from samples indexed by the Librarian. The [[Ecumene Council]] deemed this a severe violation against the [[Mantle]]. The remaining Halo rings were to be brought to the [[Capital]] and were slated to be decommissioned, as they were deemed too destructive. This turned out to be a miscalculation on the Forerunners' part, as the rampant Mendicant Bias would arrive aboard Installation 07 and take control of many of the Halo rings over the capital.<ref>'''Halo: Cryptum''', "Chapter 37"</ref> Despite heavy resistance from the Forerunner fleets, Mendicant Bias successfully fired Installation 07 in the Capital system, delivering a catastrophic blow to the Forerunner leadership for a time.{{Ref/Reuse|p272}}

While the Forerunner government had downplayed the Flood threat up until this point,{{Ref/Reuse|c235}} they were now forced to take more drastic measures in order to survive. The Ecumene Council remained in disarray after Mendicant Bias' attack. The [[Ur-Didact]] had only recently returned from a millennium of exile, but the Master Builder, before being removed from power, had managed to capture the Didact and abandon him in a Flood-infested region of the galaxy. However, the Didact had duplicated his essence to another body, creating a secondary incarnation of himself, known as the [[IsoDidact]]. This copy assumed the role of the original Didact and reassumed command of the Forerunner military. Hoping to defeat the Flood via conventional strategy, the IsoDidact reactivated his [[shield world]]s and the defense plan he had engineered thousands of years earlier.<ref>'''Halo: Cryptum''', ''page 250''</ref><ref>'''Halo: Cryptum''', ''page 341''</ref> The Forerunners scored a temporary victory as the IsoDidact's forces reclaimed Installation 07 and captured the rampant Mendicant Bias. The Ecumene Council, which had been crippled by Mendicant Bias' attack, was reinstated shortly afterward as the "New Council".<ref>'''Halo: Primordium''', ''page 374-375''</ref>

===Final years===
[[File:H4-Terminal-Flood-Fleet.jpg|thumb|300px|A fleet of infected Forerunner and Ancient Human ships.]]
The Forerunners' victory was short-lived; Mendicant Bias' defection and subsequent decapitating strike on the Old Council had marked a turning point in the course of the war. What had been a steadily growing but relatively contained infestation now rapidly exploded beyond hope of control. Using vessels and forces operated by both corrupted biologicals and AIs, supposedly marshaled during the decades Mendicant Bias and Installation 07 were missing, the Flood began to strike critical Forerunner systems in overwhelming numbers. Due to the Forerunners' previous cover-up of the Flood threat, subverted forces were initially welcomed in many systems left unaware of their true nature. Two thousand systems were rapidly infected, becoming home to [[Flood hive]]s.<ref>'''Halo: Silentium''', ''pages 183-184''</ref> Undeterred the Flood continued to spread; with the Forerunner defenses unable to stop the Flood's advance, over 500,000 star systems were infected by the Flood. The Flood soon controlled two-thirds of the ecumene; these areas were referred to as [[Burn]]s.<ref>'''Halo: Silentium''', ''String 20''</ref>

When the Flood threat began to spiral out of control, the Forerunners resorted to an ancient defensive barrier; the [[Maginot Line|Jat-Krula]], often translated as the "Maginot Line", which protected their core systems within the [[Orion complex]]. The Forerunner leadership decided to focus on the preservation of the systems within the Line while leaving the rest of the ecumene to fend for themselves.<ref>'''Halo: Silentium''', ''pages 104-105''</ref> The Forerunners mostly succeeded in holding the Flood at bay at this barrier before the very end of the war, although the Flood managed to breach the Line in several locations.<ref>'''Halo: Silentium''', ''page 193''</ref> The Forerunner [[Librarian]] and her [[Lifeworker]]s journeyed beyond this line at great personal risk, continuing their mission of indexing and documenting sentient species across the galaxy, filling every vessel possible with documented species for transit to the Ark for safety in the campaign to save all species possible from the advancing Flood.{{Ref/Reuse|h3terminals}} Over a period of four years, the [[IsoDidact]] commanded Forerunner defense operations from within the Line, leading forces combined from [[Warrior-Servant]]s and [[Builder Security]].<ref>'''Halo: Silentium''', ''page 197''</ref>

Although Mendicant Bias had been disassembled and scattered across the ecumene, the facilities in which the disparate parts of the metarch were held were eventually overrun by the Flood and Mendicant was soon reconstituted as the commander of the Flood's fleets.<ref>'''Halo: Silentium''', ''pages 267-268''</ref> Furthermore, as the Flood gained more biomass, it continued to develop into more potent and dangerous forms; massive compound mind nodes known as [[Key Mind]]s were formed as entire planets were assimilated. The raw computing power of these enormous collectives could outwit even the most advanced Forerunner AIs.<ref>'''Halo: Silentium''', ''pages 186-187''</ref>

The Flood became more virulent as the infection took up more aspects; the most prominent of these was the [[logic plague]], the ability to subvert and corrupt Forerunner artificial intelligences. This metaphysical form of corruption could eventually be perpetuated by any Flood form or infected AI, and rapidly spread across the Forerunners' data networks. The Forerunner [[Juridical]]s were forced to halt all legal proceedings as their principal network and many of their primary agents—[[Catalog]]—were overtaken by the logic plague.<ref name="s214">'''Halo: Silentium''', ''pages 214-215''</ref> Even in the final years of the war, the Forerunners were determined to salvage infested vessels and purge them of both biological and software infection wherever possible; only a minute fraction of these attempts were ultimately successful, eventually resulting in the Forerunners terminating these efforts completely and opting for complete destruction of all infected ships.{{Ref/Reuse|s214}}

In this late stage of the war, the Flood became powerful enough to use [[neural physics]]-based technology, allowing them to take control of the numerous [[Precursor]] artifacts, such as [[star road]]s, that had lain dormant across the galaxy for millions of years. The Forerunners did not possess any formidable defense against the sheer power and destructive capability of the Precursor constructs, which were capable of effortlessly dealing widespread devastation on entire Forerunner fleets. After disabling their weapons and shields, the star roads corralled Forerunner vessels into smaller units to allow their crews to be parasitized by the Flood. Less than one half of one percent of Forerunner vessels attacked this way were able to self-destruct before they were overwhelmed.{{Ref/Reuse|s214}} The Precursor constructs were also capable of manipulating space-time to become unsuitable for Forerunner slipspace travel and leaving entire fleets stranded or lost in anomalous slipspace transit.<ref>'''Halo: Silentium''', ''pages 235-236''</ref> During this time, entire planets such as [[Triniel]] committed planet-wide mass suicide to deprive the Flood access to their biomass as potential hosts. The Flood would then leave the dead world untouched as there was nothing of interest on the planet for them despite entire Forerunner cities being left intact.<ref>'''[[Halo: Renegades]]''', ''pages 202-203''</ref>

===Endgame===
{{Quote|We seek security in the [[Domain]] and the example of the [[Mantle]]. We who are about to kill seek forgiveness. We treasure the truth of our error, that in future error will pass from us, and from the lives of all who come after.|[[Faber]], the [[Master Builder]], chanting before unleashing [[Omega Halo]] on [[Path Kethona]].<ref>'''Halo: Silentium''', ''page 271''</ref>}}
[[File:HM Ark destruction.png|thumb|left|300px|The destruction of the Greater Ark.]]
Having evacuated the remaining Forerunner population to safety, Forerunner fleets were repositioned to defend a region of four themas, nearly overrun by the Flood. Despite attaining a [[Battle of the 78th Thema|rare victory]] at the 78th Thema, the Forerunners continued to lose ground in most engagements. All surviving vessels from the last Forerunner fleets were eventually assigned under the command of the metarch-class AI [[Offensive Bias]], designed to replace and counter the rampant Mendicant Bias.<ref>'''Halo: Silentium''', ''page 215''</ref> In a decisive last stand beyond [[Jad Sappar]], the last combined Forerunner fleet faced massive swarms of infested ships, supported by thousands of star roads.<ref>'''Halo: Silentium''', ''pages 222-223''</ref>

With the defenses of the Capital and the entire [[Orion complex]] failing and the Forerunner fleets across the galaxy being steadily ravaged by the Flood, strategic command of the ecumene was placed in the [[greater Ark]],{{Ref/Reuse|s214}} which eventually held the last remnants of the ecumene aside from minor pockets of survivors across the galaxy.<ref>'''Halo: Silentium''', ''page 327''</ref> The Librarian's biological specimens—including her core human population—once held on the Ark's surface were moved to the nearby [[Omega Halo]], which, along with [[Installation 07]], was the last of the Master Builder's original Halos.<ref>'''Halo: Silentium''', ''pages 237-238''</ref> A handful of Forerunner military commanders survived to retreat to the greater Ark, managing to bring a small number of warships with them to defend what was now the ecumene's last bastion.<ref>'''Halo: Silentium''', ''page 245''</ref>

The remaining Forerunner leadership gathered at the greater Ark, including the Ur-Didact, who had been recovered from deep within the Burn by the Master Builder. Soon after their arrival, the Ark came under siege by Mendicant Bias and its fleet of Flood-controlled ships and star roads. Out of desperation, the remnants of the Council restored the Master Builder to command, as he was the only one with a realistic vision on how to stop the Flood: the Halo Array, which targeted all neural structures—including the Flood and their Precursor structures, thus capable of stopping them once and for all. While this was true, it was too little, too late, and he knew this better than anyone: he revealed the location of the [[Installation 00|lesser Ark]] to the IsoDidact and ordered him there.<ref>'''Halo: Silentium''', ''String 29''</ref> 

The [[Battle of the greater Ark|penultimate battle of the Forerunners]] was bitterly short: Omega Halo's primary weapon, having never been upgraded, could only fire in one direction and it was able to fire only once, tearing a hole in the approaching Flood wave and striking the [[Large Magellanic Cloud]]; while seemingly devastating, the Flood paused only momentarily to restore their line. Further delayed only slightly by the desperate defense offered by [[Offensive Bias]], Mendicant Bias and the Flood fleet destroyed Omega Halo and the greater Ark, along with most of the Forerunner fleet.<ref>'''Halo: Silentium''', ''String 33''</ref>

In the chaos just before the battle was joined, the Ur-Didact—who had been driven mad by the [[Gravemind]]—used a [[Composer]] to [[Mind transfer|harvest]] the essences of the entire human population of Omega Halo, much to the horror of the Librarian who had placed all of her hope in humanity. The Didact planned to use the essences of both the humans and his own [[Promethean]]s to build an army of [[Promethean Knight|mechanical warriors]], which he believed could fight an extended campaign against the Flood. This was a grave transgression in the eyes of the Librarian, who had already laid plans for humanity as the [[Reclaimer|successors]] to the Forerunners. In order to stop the Ur-Didact, the Librarian forcibly incapacitated him and imprisoned him within the shield world [[Requiem]].<ref name="h4terminals">'''Halo 4''', [[Terminal (Halo 4)|Terminals]]''</ref>

===Firing of Halo===
{{Main|Great Purification}}
{{Quote|Something is wrong...at night I can see it--flitting shadows--black against the stars. Thousands of ships! Not spiraling outward, but heading for the line! This is the tipping point, Didact. It's no longer feeding. It's coming for you.|The Librarian to the IsoDidact.{{Ref/Reuse|h3terminals}}}}
[[File:HaloFiring.png|thumb|300px|The firing of the [[Halo Array]], leading to the end of the war.]]
The IsoDidact (rescued from the destruction of Omega Halo by [[343 Guilty Spark|Monitor Chakas]]), Offensive Bias, and the remaining Forerunners headed to the [[Installation 00|lesser Ark]], along with the surviving biological specimens from the greater Ark. This formerly secret installation contained the Forerunners' final weapon: the newer [[Halo Array]], which would purge the galaxy of sentient life, depriving the Flood of all biomass that they could consume, thus halting them. The seven rings were deployed in their designated locations across the galaxy, and while the firing preparations were being conducted, Mendicant Bias and the Flood prepared to assault the Ark. In order to give the IsoDidact time to fire the rings, the Librarian journeyed to Earth, broadcasting a feint message to draw the Flood there. Ignoring the IsoDidact's pleas to return to the Ark, the Librarian calmly embraced her inevitable demise in the savanna near [[Mount Kilimanjaro]], overlooking the construction of the [[Portal at Voi|Portal to the Ark]].{{Ref/Reuse|h3terminals}}

To ensure enough time for the Halo Array to fire, the IsoDidact ordered Offensive Bias and all that remained of the Forerunner fleets to delay Mendicant Bias' fleet.<ref name="silentium">'''Halo: Silentium''', ''String 38''</ref> While the IsoDidact initiated the Halo Array's activation sequence, the Flood fleet engaged the last Forerunner fleet in [[Battle of the Maginot Sphere|a massive naval battle]]. Feigning incompetence and using delaying tactics, Offensive Bias and his fleet held off the Flood as the Halos activated, exterminating all sentient life in the Milky Way galaxy. With the previously Flood-controlled ships now adrift, Offensive Bias annihilated Mendicant's remaining fleet within minutes. Offensive then proceeded to extract the last remaining shard of Mendicant Bias from one of its core ships and return it to the lesser Ark.{{Ref/Reuse|h3terminals}}
{{Clear}}
==Aftermath==
The Halo effect purged the galaxy of all sentient life, eliminating the threat of the Flood as it was deprived of available biomass and its collective consciousness. All Precursor artifacts and structures, composed of abstract [[neural physics]] construction, were likewise destroyed. These included the [[Domain]], a metaphysical repository of knowledge treasured by the Forerunners as the source of all their cultural heritage and ancestral wisdom.<ref>'''Halo: Silentium''', ''pages 322-323''</ref>

The surviving Forerunners on the Ark, under the leadership of the IsoDidact, imprisoned what was thought to be the last component of Mendicant Bias deep within Installation 00.<ref name="trial">'''[http://www.youtube.com/watch?v=a3YLl2NLVFA The Trial of Mendicant Bias]'''</ref> The lifeforms sheltered on the Ark were eventually returned to their homeworlds and [[reintroduction|reintroduced]] to their native ecosystems, now free of the Flood, by the remaining Forerunners and their automatons; this process was led by the new [[Lifeshaper]], [[Chant-to-Green]].<ref name="rebirth">'''[[Rebirth]]'''</ref>

Despite the Lifeworkers' best efforts, the firing of the Halos resulted in mass extinction events on countless worlds across the galaxy; most prominently those the Forerunners had never had the time or resources to index. On many planets, Lifeworkers had to prioritize which species to save; for example, it was estimated that only one-thousandth of [[Earth]]'s large species would survive.{{Ref/Reuse|s27}} Around four years before the firing of the Halos, 123 technologically capable species had been indexed; however, a number of these were doomed to perish due to the Lifeworkers' limited resources,<ref>'''Halo: Silentium''', ''page 18''</ref> combined with the devastation of the preserves on the [[greater Ark]] and [[Omega Halo]]. Many species also died out as a result of planetary ecosystems failing to properly recover after their reseeding, during the subsequent period known as [[the dark time]].{{Ref/Reuse|bestiarum}}

After this reseeding effort was finished the surviving Forerunners left the galaxy,<ref>'''[[Halo Encyclopedia (2009 edition)]]''', ''pages 16, 28, 171, and 289''</ref> vowing to exclude themselves from the affairs of other species out of guilt over their failure as galactic custodians.{{Ref/Reuse|rebirth}} The Forerunners left the Mantle for humanity to [[Reclaimer|reclaim]]<ref>'''Halo 4''', campaign level ''[[Reclaimer (level)|Reclaimer]]''</ref> as the Precursors had intended millions of years earlier.{{Ref/Reuse|s173}}
{{Clear}}

==Gallery==
<gallery>
File:Forerunner Meeting.jpg|A group of Forerunners discuss the Flood.
File:Ships flood.png|Flood-infected Forerunner ships.
File:Old_HW_Armament.jpg|Forerunner combatants facing a horde of Flood.
File:TerminalArkArray.jpg|The Halo Array at Installation 00, awaiting its deployment across the galaxy.
File:Keysip.png|Keyships serving out their mission to reseed life throughout the galaxy.
</gallery>

==List of appearances==
*''[[Halo 2]]'' {{Fm}}
*''[[Iris]]'' {{Mo}}
*''[[Halo 3]]''
**''[[Terminal (Halo 3)|Terminals]]'' {{Mo}}
*''[[Halo Legends]]''
**''[[Origins]]'' {{1st}}
*''[[Halo: Cryptum]]''
*''[[Halo: Combat Evolved Anniversary]]'' 
**''[[Terminal (Halo: Combat Evolved Anniversary)|Terminals]]''
*''[[Halo: Primordium]]''
*''[[Halo 4]]''
**''[[Terminal (Halo 4)|Terminals]]''
*''[[Halo: Silentium]]''
*''[[Rebirth]]'' {{Im}}
*''[[Halo: Broken Circle]]'' {{Mo}}
*''[[Halo: Last Light]]'' {{Mo}}
*''[[Halo 5: Guardians]]'' {{Mo}}
*''[[Halo Mythos: A Guide to the Story of Halo]]''
*''[[Halo: Fractures]]''
**''[[Promises to Keep]]'' {{Mo}}
**''[[Defender of the Storm]]''
*''[[Halo Wars 2]]'' {{Mo}}
*''[[Halo: Renegades]]'' {{Mo}}
*''[[Halo: Point of Light]]'' {{Mo}}
*''[[Halo Infinite]]'' {{Mo}}
*''[[Halo: Epitaph]]''

==Sources==
{{Ref/Sources|2}}

{{Forerunner-Flood War}}
[[Category:Wars]]