Editing Halo Array

{{Status|Canon}}
{{Center|"Halo" redirects here. For other uses, see [[Halo (disambiguation)]].}}
[[File:TerminalArkArray.jpg|thumb|right|300px|The Array at [[Installation 00]], just before their departure to firing sites across the galaxy.]]
{{Quote|Halo doesn't kill Flood, it kills their ''food!'' Humans, Covenant, whatever—we're all equally edible! The only way to stop the Flood is to starve them to death. And that's exactly what Halo is designed to do: wipe the galaxy clean of all sentient life!|[[Cortana]] during the [[Battle of Installation 04]]}}.{{Ref/Level|Id=TB|HCE|Two Betrayals}}

The '''Halo Array''', sometimes known simply as '''Halo'''<ref>''[[Halo: Warfleet]]'', p. 92</ref> or '''the Array''',<ref>'''[[Halo 3]]''', ''[[Terminal (Halo 3)|Terminal Four]]''</ref><ref>'''[[Halo: Combat Evolved Anniversary]]''', ''[[Terminal (Halo: Combat Evolved Anniversary)|Terminal Two]]''</ref> is a network of colossal ring-shaped superweapons individually known as '''Halos''' or '''Halo rings''', constructed by the [[Forerunner]]s.{{Ref/Level|Id=TC|HCE|The Truth and Reconciliation}} The Halos were also referred to by the [[Covenant]] as the '''Sacred Rings''',<ref>'''Halo: The Flood''', page 38</ref>{{Ref/Level|Id=gravemind|H2|Gravemind_(level)}} and labeled as '''Installations''' or infrequently referred to as Fortress Worlds<ref>'''Halo: The Flood''', ''page 193''</ref> by the Forerunners and their [[monitor]]s.

The first array of twelve Halos was constructed by order of [[Master Builder]] [[Faber]] circa [[98,445 BCE]] with the intent of being an ultimate weapon, one that would secure the preeminence of the [[Builder]] [[rate]] in Forerunner society.<ref name="c274">'''Halo: Cryptum''', ''page 274''</ref> Later, the weapons would be refined further and a new array of six smaller and significantly more lethal installations was constructed; the newer Halos are known as the "neoteric" rings.{{Ref/Site|Id=neoteric|URL=https://www.reddit.com/r/halo/comments/70wbxc/return_to_the_denomination_installation_04_b_c/dn76nzc/|Site=Reddit|Page=Return to the denomination. Installation 04 (B), (C). Canonically. 343 PLS|D=18|M=9|Y=2017}} Eventually, eleven were destroyed and/or lost while the remaining [[seven]] were used by the Forerunners as a last resort when combating the parasitic [[Flood]].{{Ref/YouTube|Id=Lorestream|fYaxRoAf96s|HALO|Halo Lore Stream: The Halo Array|Y=2018|M=04|D=06|343 discuss the the Halo Array}} All [[sentience|sentient]] beings in the galaxy were killed, robbing the Flood of hosts and starving it to death.

In addition to serving as weapons of last resort, Halo installations are also research facilities dedicated to containing and studying many different kinds of life forms. The life forms that were hand-selected by the [[Librarian]] included marine life, fauna, and land vertebrates. With the Master Builder's permission, the Librarian would research each animal to detect if their bodies reacted to Flood infection. The research on the animals would be more deeply analyzed if they did become infected. The Librarian's studies also helped determine if the rings could be used to repopulate the galaxy as part of the [[Conservation Measure]].{{Ref/Reuse|Lorestream}}<ref name="c313">'''Halo: Cryptum''', ''pages 313, 334''</ref>

==Background==
[[File:Halo Surface.jpg|thumb|200px|A section of a Halo's surface.]]
{{Quote|After exhausting every other strategic option, my creators activated the rings. They, and all additional sentient life in three radii of the galactic center, died, as planned.|[[343 Guilty Spark]] during the [[Battle of Installation 05]]}}.{{Ref/Reuse|great journey}}
As it is known in modern times, the Halo Array is a network of seven ring-shaped megastructures created by the Forerunners, designed to exterminate all sentient life within the Milky Way galaxy.{{Ref/Level|Id=great journey|H2|The Great Journey}} Built following the [[Human-Forerunner War]], these ringworlds were later used as a last resort against the Flood, a parasitic extra-galactic species that threatened to consume every sentient life-form in the galaxy. By activating the rings, the Forerunners wiped out every sentient being in the galaxy, effectively starving the Flood to virtual extinction, though specimens were kept in a number of Forerunner [[Flood containment facility|containment facilities]], including the Halo installations themselves.{{Ref/Level|Id=library|HCE|The Library}}

A total of eighteen Halo rings existed during the reign of the Forerunners; an older array of twelve 30,000-kilometer-wide rings produced by the [[greater Ark]] and six 10,000-kilometer rings, constructed at the newer [[Installation 00|lesser Ark]]. Of these, only seven survived to be included in the final Array. The Halos were originally deployed in orbit over large gas giants.<ref name="gas giants">'''Halo: Silentium''', ''page 237''</ref> However, as of [[2557]], [[Installation 03]] orbited a rocky planet.{{Ref/Level|Id=h4composer|H4|Composer_(level)}} Installation 04 maintained an atmospheric [[Threshold gas mine|mining facility]] in its anchor planet [[Threshold]]'s atmosphere until [[Battle of the Threshold gas mine|it was destroyed]] by the [[Covenant]].{{Ref/Level|Id=The Oracle|H2|The Oracle}}

Though separated by thousands of light-years, the installations are networked together and capable of remote activation at [[Installation 00|the Ark]], their [[intergalactic space|extragalactic]] construction foundry. Each Halo installation has a maximum effective range of 25,000 light-years in every direction.<ref>'''Halo: Combat Evolved Anniversary''', ''[[Terminal (Halo: Combat Evolved Anniversary)#Terminal 8|Terminal 8]]'' (''"25,000 light years. That is the effective range of this installation."'')</ref><ref name="radius">'''[[Halo: Combat Evolved]]''', level ''[[Two Betrayals]]'', 343 Guilty Spark: ''"Technically, this installation's pulse has a maximum effective radius of twenty-five thousand light years."''</ref> The method utilized by the array to conduct this "mass sterilization protocol"<ref>'''[[Halo: Combat Evolved]]''', level ''[[The Library]]'', 343 Guilty Spark: ''"Why the Flood is, naturally, simply too dangerous to release, and mass sterilization protocols may again need to be enacted."''</ref> involves the superluminal conveyance of a burst of cross-phased super-massive neutrinos, tuned to emit a harmonic frequency that destroys the nervous system of any life form within range. Simpler organisms lacking a neural system are unaffected, along with inanimate structures. [[Precursor]] technology, however, is extremely susceptible to damage from the Halo effect due to its quasi-living [[neural physics]] composition.{{Ref/Reuse|c274}}<ref>'''Halo: Cryptum''', ''page 132''</ref>

[[File:H2A - Halo Array hologram.jpg|left|thumb|250px|Readout of the seven Halos.]] 
The Halo Array in its entirety has been fired only once in known history, approximately 100,000 years ago, by the [[IsoDidact]] in order to stop the Flood from overwhelming the galaxy. All beings in the Array's effective range, including Forerunners themselves, were wiped out by the Array's pulse,{{Ref/Reuse|great journey}} with the exception of those who took refuge on the [[shield world]]s. A number of Forerunners survived at the lesser Ark but chose to exile themselves from the galaxy.<ref name="rebirth">'''Halo: Rebirth'''</ref> The array has come close to activation four times since; Installation 04 was almost activated by the [[John-117|Master Chief]], Installation 05 was activated by Commander [[Miranda Keyes]] at the behest of the [[Jiralhanae]] [[Chieftain of the Jiralhanae|Chieftain]] [[Tartarus]], [[Avery Junior Johnson|Sergeant Johnson]] was forced by the [[Prophet of Truth]] to activate the Array from the Ark, and [[Bobby Kodiak]] was forced by [[000 Tragic Solitude]], the Monitor of the Ark, to activate the Halo Array from the Ark as a revenge. None of these attempts were successful; the first was stopped by Cortana, while the other three attempts were halted by UNSC and [[Swords of Sanghelios|Sangheili]] intervention. A [[Installation 08|replacement]] Halo for the destroyed Installation 04 was partially activated outside of the galaxy, but before it could fire the Halo ring shook itself to pieces with the resulting explosion destroying the ring, damaging the Ark, and heavily damaged the Flood back into a feral stage without a Gravemind.{{Ref/Level|Id=halo3halo|H3|Halo_(Halo_3_level)}}

Each of the Halo installations manufactured at Installation 00 is given a sequential designation number based on their order of construction, beginning from 01,{{Ref/Reuse|neoteric}} and is overseen by a single [[monitor]]. The monitors are given control of the Installations' [[Sentinel]] automatons, from [[Sentinel Aggressor|Aggressors]] to [[Constructor]]s and [[Enforcer]]s, and are responsible for containing the Flood test subjects in their [[Flood research facility|research facilities]] and protecting the Halo from intruders.

The Array also encompasses [[Installation 00]], an extra-galactic construction facility that can create replacement installations in the event that one is destroyed. All Halos can also be remotely activated from the Ark without being subjected to their effects, as the megastructure is out of the Array's range.{{Ref/Level|Id=thecovenant|H3|[[The Covenant (level)|The Covenant]]|Quote='''343 Guilty Spark''': ''"The Ark is out of range of all the active installations!"''}} The Forerunners also built [[shield world]]s as a means to escape the effect without having to leave the galaxy.{{Ref/Novel|GoO|Page=??}}
{{clear}}

==History==
===Construction===
[[File:ForerunnerObserver.jpg|thumb|250px|A Forerunner observes the construction of a Halo.]]
The first Halos were constructed by the [[Master Builder]] [[Faber]] and his [[Builder]]s in the millennia after the [[Flood]] was first encountered in the Milky Way, only to eventually retreat, seemingly due to [[prehistoric human civilization|early humanity]]'s efforts. The most extreme faction of Builders, which at the time controlled the [[Ecumene Council]], claimed that more extreme measures should be used to protect the galaxy against a possible Flood resurgence and proposed building the Array for this purpose. The initial iterations of the weapon system that would eventually become Halo did not share the circular shape of the final installations.<ref>'''Halo: Cryptum''', ''page 243''</ref> Although they faced strong opposition from the [[Promethean]]s, led by the [[Ur-Didact|Didact]], for thousands of years, the faction eventually won the approval of the Council and commenced work on the Array.{{Ref/Reuse|c274}} Several prototypes of the Halos were constructed and powered by their host facilities, with [[Prototype Halo installation|one such installation]] orbiting a rogue planet.<ref name="SoI5">'''[[Halo: Shadow of Intent]]''', ''pages 5-10'' (Google Play edition)</ref>

However, at this point, the [[Librarian]] went to the Council and invoked the Mantle, stating that the Halos should be used as biological preserves in the [[Conservation Measure]], a plan to repopulate the galaxy should the Array ever be activated. The Council approved her request, and ordered that the Halo installations be constructed to have a range of natural environments for the Lifeworkers to preserve their biological specimens in. The Builders also agreed, seeing the inclusion of biological preserves as an effective means of competing with the Didact's shield worlds which incorporated similar measures.<ref name="s44">'''Halo: Silentium''', ''page 44''</ref> However, the Master Builder later altered the initial plan, and his researchers began to use these specimens for a series of brutal experiments involving Flood infection.<ref>'''Halo: Primordium''', ''page 188-190''</ref>

Twelve Halos, each 30,000 kilometers in diameter, were originally commissioned by Master Builder Faber and constructed by the [[guild]] of [[Bornstellar's father]] at the [[greater Ark]], the first Ark installation to be constructed. Only one of these original rings ultimately survived to be used in the Forerunners' final plan; this ring was designated [[Installation 07]]. Later on, an improved, separate array of six installations was constructed at the [[Installation 00|lesser Ark]],<ref>'''Halo: Cryptum''', ''page 329'' (''"Slowly it dawned on me that I was looking upon another array of installations: six rings, each rising from one of the petals of an enormous flower."'')</ref><ref name="s250">'''Halo: Silentium''', ''pages 250-251''</ref> although the construction of the second Ark and its more powerful Halos was delayed by the Council for some time to prevent the Builders from becoming too powerful.<ref>'''Halo: Silentium''', ''page 45''</ref>

In the later stages of the construction of the first Halos, a Builder named [[Maker-of-Moons]] was assigned to improve upon their designs. The first test deployments had proven the original rings to be unstable and too large to be practically deployed, generating enormous [[Slipstream space#Reconciliation|particle reconciliation]] debt when moved. The original Ark also had several flaws, including the inability to construct smaller installations. Although initially reluctant to admit these defects,<ref name="maker">'''Halo: Silentium''', ''page 91''</ref> the Master Builder, informed by Maker's analysis, commissioned a new Ark and a series of new, more efficient rings several millennia after the first Halos were made; the Builders promoted this as a means to save even more species while being able to create more Halos. The new Ark, known as the lesser Ark or [[Installation 00]], and its six new Halos were constructed in secret,{{Ref/Reuse|s44}} their location known only to the Master Builder.<ref name="s270">'''Halo: Silentium''', ''page 270''</ref>

The final Array, activated at the conclusion of the Forerunners' conflict with the Flood, comprised seven rings, each 10,000 kilometers in diameter, one of them being the reduced Installation 07.<ref name="s314">'''Halo: Silentium''', ''page 314''</ref>

===Forerunner-Flood war===
[[File:FoM.jpg|thumb|left|250px|The original Halos gathered in orbit around [[Maethrillian]].]]
The first test of a Halo installation was conducted by [[Mendicant Bias]], who fired [[Installation 07]] in [[Charum Hakkor system|the system]] of [[Charum Hakkor]] and [[Faun Hakkor]] on a low power setting, destroying all of the sentient life on the latter planet and inadvertently releasing the [[Primordial]], an extant [[Precursor]] entity, from captivity on the former planet. Mendicant Bias then brought the released being to the Halo for study and began a 43-year-long interrogation of it. Eventually, Mendicant Bias disappeared with Installation 07 after being [[logic plague|corrupted]] by the Primordial.

Following the use of a second Halo by Master Builder Faber to suppress [[Battle of Janjur Qom|a rebellion]] on the [[San'Shyuum]] homeworld of [[Janjur Qom]], the other eleven Halo installations were taken to the Forerunner [[Capital]] during the tribunal against Faber, where it was to be decided whether to decommission them. However, in the midst of the trial, Mendicant Bias, turned rampant by the Primordial, appeared with Installation 07, which had gone missing following the ancilla's corruption and [[Fate of Maethrillian|assaulted the Capital]]. The AI attempted to seize control of the remaining Halos and fire them, but was only able to control five out of the twelve. One of those five was destroyed by the combined tidal forces of the Capital, the firepower of local Forerunner fleets, and the stress of a recent [[slipspace]] transition. The seven Halos that Mendicant Bias was unable to control were recalled to Installation 00 via a [[slipspace portal]], yet only [[Omega Halo|one]] escaped before the portal collapsed, with the other six breaking up in slipspace.

Installation 07 jumped into a distant system on a pre-designated destructive collision course with [[Wolf-faced planet|a planet]]—a security measure put in place in the event that it fell out of Forerunner control. The installation was eventually reclaimed by the IsoDidact's forces, and it survived the passage of the planet despite taking heavy damage. A significant amount of the ring's superstructure was discarded, reducing its size to 10,000 kilometers, in order to allow it to perform a successful slipspace jump to the [[greater Ark]]. The installation's surviving biological specimens were transported on the Ark and the Flood outbreak on the ring was contained. The ring was refitted to enable it to function in concert with the six final Halos and deployed to its final station in the galaxy; the distribution of the final Halo Array would follow several years later.{{Ref/Reuse|s314}}

During the battle at the Capital and the years that followed, all but one of the original twelve rings—[[Omega Halo]]—apart from the repurposed Installation 07 were hunted down and destroyed by the Flood.<ref>'''Halo: Silentium''', ''pages 234, 237''</ref> In the final hours of the Forerunner-Flood war, the ecumene's leadership retreated to the greater Ark, also home to Omega Halo. When a [[Battle of the greater Ark|Flood attack]] became imminent, it was decided that the IsoDidact go to the lesser Ark where he would deploy and fire the final Halo Array. Before relinquishing the coordinates to his secret Ark,{{Ref/Reuse|s270}} the Master Builder met the IsoDidact in the control room of Omega Halo and fired the ring, obliterating a small portion of the [[star road]]s laying siege on the Ark and cleansing the [[Large Magellanic Cloud]] of life.<ref name="s273">'''Halo: Silentium''', ''page 273''</ref>

====Activation====
{{Main|Great Purification}}
[[File:Array.png|thumb|right|300px|Installation 00 sending the Halo Array through a [[slipspace portal]] during the [[Forerunner-Flood war]].]]
The Flood and the star roads destroyed both Omega Halo and the greater Ark, but the IsoDidact managed to escape to Installation 00 to fulfill his mission. Arriving at the lesser Ark, the IsoDidact had the rings' Index collection distributed to their respective installations aboard a Lifeworker vessel over the Ark. The installations' primary monitors were also formally given their assignments to their final posts. Each monitor received a new name and numeric designation, each intended to serve as a form of memorial to the Forerunners.<ref>'''Halo: Silentium''', ''page 313''</ref> With the assistance of [[Offensive Bias]], the IsoDidact deployed the remaining six Halos from [[Installation 00 Citadel|the Ark's Citadel]]. Together with Installation 07, these installations comprised the final Halo Array of seven rings.{{Ref/Reuse|s314}}

[[File:HaloFiring.png|thumb|left|250px|The Halo Array fires, ending the conflict.]]
As Mendicant Bias and the Flood prepared their [[Battle of the Maginot Sphere|final assault]] on the lesser Ark in order to stop the firing of the Halos, the IsoDidact activated the Array. [[Installation 04]] was first in the Array to fire, with the others following sequentially as their fields intersected.<ref name="sil326">'''Halo: Silentium''', ''pages 326-327''</ref> The pulse covered the entire galaxy, killing all sentient life within range and destroying the Precursors' [[neural physics]] architecture, including the [[Domain]] the Forerunners used to hold dear.<ref>'''Halo: Silentium''', ''pages 322-323''</ref> Whether the pulse would destroy star roads and other Precursor artifacts in faster-than-light transit was uncertain even to the Forerunners themselves, due to the largely unknown mechanisms of Precursor superluminal travel.<ref name="s312">'''Halo: Silentium''', ''page 312''</ref> However, their total destruction seems apparent from the fact they were no longer in evidence when the Forerunners repopulated the galaxy.{{Ref/Reuse|rebirth}}

It was later discovered that a species called the [[Xalanyn]] had somehow survived the firing of the Halo Array. Frightened that the Xalanyn would eventually become the dominant species of the galaxy and claim the [[Mantle of Responsibility]], the Forerunners brought [[Installation 07]] into orbit of the Xalanyn homeworld under the pretense of a meeting and imprisoned them on the ring for containment and study.{{Ref/Game|Hi|Detail=[[Audio log (Halo Infinite)|Audio logs]]}}

===Post-activation===
The seven Halos then remained relatively dormant for approximately one hundred thousand years, though at least [[Installation 05]] experienced a major Flood outbreak, while [[Installation 04]] was visited briefly by other species,<ref>''"[[Conversations from the Universe]]"''</ref> including a [[unidentified alien vessel|major crash-landing]] in [[40,000 BCE]].<ref>'''Halo: Combat Evolved Anniversary''', ''[[Terminal (Halo: Combat Evolved Anniversary)|Terminals 5-6]]''</ref>

The Array's activation caused catastrophic damage to ecosystems across the galaxy, with innumerable species both sentient and non-sentient rendered extinct. The dissolving of dead bodies thanks to [[solute]] eventually showed up on the fossil record, and was labeled by scientists as the [[Ross-Ziegler Blip]]. This curious gap was dismissed as an anomaly caused by spatial distortion until [[human]]ity discovered the Array in [[2552]]. Several species indexed by the [[Library Project]] did not survive [[reintroduction]] to their homeworlds, and those that did were all reverted to a [[Technological Achievement Tiers#Tier 7: Pre-Industrial|Tier 7]] technological state. The mostly uneventful period starting after the firing of the Halos was known as the [[dark time]].

The [[Covenant]], a theocratic multispecies alliance, was founded on the misguided belief that the Halo Array was actually the source of a "Divine Wind" that allowed the Forerunners to transcend the physical. By activating the Array, they too could embark on this "[[Covenant religion|Great Journey]]" and join the Forerunners in godhood.

===Rediscovery===
[[File:H2A-AlphaHaloDestruction.jpg|250px|right|thumb|The destruction of Installation 04.]]
Eventually, the stellar coordinates of [[Installation 04]] were discovered through the combination of a [[Sigma Octanus IV artifact|crystal artifact]] on [[Sigma Octanus IV]] and a [[Babd Catha Forerunner vessel|huge Forerunner artifact]] buried under the surface of [[Reach]]. The coordinates were utilized by the {{UNSCShip|Pillar of Autumn}}'s shipboard [[AI]] [[Cortana]] to escape from the [[Fall of Reach]]. The cruiser arrived over the Installation's orbit and was subsequently shot down by Covenant ships. Most of the ship's combat personnel escaped and made landfall on the artificial construct, triggering the [[Battle of Installation 04]].

During their investigations on Installation 04, the Covenant encountered a [[Flood containment facility]] and unknowingly released the dormant Flood; they quickly, but only partially, reestablished containment. Soon, a squad of [[UNSC Marine Corps|Marines]] led by [[Captain (Navy)|Captain]] [[Jacob Keyes]] accidentally broke quarantine again, expecting to find a large Covenant weapons cache. The human-waged guerrilla war quickly turned into a massive four-way battle between [[United Nations Space Command|UNSC]] forces, the Covenant, [[Sentinel]]s led by [[343 Guilty Spark]], and the Flood.

[[File:Halo Firing.png|250px|left|thumb|The partially constructed Installation 08 hovering over the Ark.]]
The battle finally culminated when [[SPARTAN-II program|Spartan]] [[John-117]] detonated the [[fusion engine]]s of the ''Pillar of Autumn'' on the surface of the installation, which compromised the structural integrity of the ring. The gravitational momentum and inertia still perpetuating the ring in orbit around [[Threshold]] then tore the ring apart. The remains of Installation 04 were scattered as debris in space. The explosion sent massive chunks of the ring careening into [[Basis]]; the moon suffered a constant bombardment of debris from the ring after its destruction.<ref>'''Halo 2''', multiplayer level ''[[Burial Mounds]]''</ref>

After escaping the [[Battle of Tribute]], a UNSC [[freighter]], ''[[Floral Express]]'', discovered [[Installation 03]] on October 8, 2552. By October 25 neutralization protocols had been established.<ref>''[[Eleventh Hour reports]]'' - ''#5''</ref>

Later, the Covenant discovered a third Halo, [[Installation 05]]. On this Halo, the Flood had already been released and much of the ring had been compromised, including its monitor, [[2401 Penitent Tangent]]. Soon, [[Battle of Installation 05|another four-way conflict]] began. The battle ended in the Flood manifesting a [[Gravemind]] and successfully escaping the ring aboard the infected {{UNSCShip|In Amber Clad}}. The ring was nearly activated by [[Tartarus]], the [[Chieftain of the Jiralhanae|Chieftain]] of the [[Jiralhanae]], but [[Commander]] [[Miranda Keyes]] pulled the [[Activation Index]] out of the installation's core at the last moment, causing all six functional installations to go into "standby mode", ready for remote activation from the Ark.

The human survivors returned to [[Earth]] and resumed their fight against the Covenant, who had uncovered a large structure on Earth, which they assumed to be the Ark. The Covenant landed the [[keyship]] ''[[Anodyne Spirit]]'' in the center of the structure, activating it. However, the structure was soon revealed not to be the Ark, but [[the Portal|a generator]] of a portal to the actual [[Installation 00|Ark]], a massive artificial world located outside the galaxy. Human and [[Swords of Sanghelios|Sangheili]] forces proceeded through the portal to the newly-discovered installation to prevent the Covenant from activating the remaining Halo rings remotely. Eventually, the Gravemind arrived at the Ark aboard [[High Charity]], the Covenant's capital city, which had been turned into a Flood hive. The hive crashed onto the installation, releasing the Flood.

Soon, 343 Guilty Spark, John-117, and [[Arbiter]] [[Thel 'Vadam]] discovered that the Ark had been constructing a [[Installation 08|new Installation 04]], to replace the one which had previously been destroyed. This new installation was only days from being completed. The humans decided to activate the new ring to stop the Flood, resulting in the incomplete ring destroying itself,<ref>'''[[Halo: The Essential Visual Guide]]''', ''page 14''</ref> severely damaging the Ark in the process.<ref name="hitd c2">'''Halo: Hunters in the Dark''', Chapter 2</ref>
{{Clear}}

===Post-Covenant War===
[[File:HSS-Infinity-Halo.png|thumb|250px|The {{UNSCShip|Infinity}} approaches a Halo installation.]]
By [[2553#January|January 2553]], the UNSC had begun an active search for the remaining Halo installations, with the intent to decommission them.<ref>'''Halo: Glasslands''', ''page 50''</ref> By at least [[2557|July 2557]], UNSC scientists were studying the Array for decommissioning, with facilities at Installations 03 and 05. Installation 00 was scouted by both automated probes and the ONI vessel {{UNSCShip|Rubicon}}, which was lost several days after its arrival due to the actions of [[343 Guilty Spark]].{{Ref/Novel|Pri}}

[[Installation 07]] was discovered in early [[2555]] due to records found on [[Sarcophagus]] by Dr. [[Luther Mann]] with an ONI research group stationed on the ring immediately afterward. A crisis occurred when it was discovered that Installation 07 — as well as the other Halos — were counting down to activation in five weeks from March 8, 2555. As the stand-by failsafe protocol had never been deactivated, it was realized that the Ark was the only location where the Array could've been activated. With the help of [[Huragok]] [[Drifts Randomly]], the [[Portal at Voi]] was reactivated, but Earth came [[Invasion of Earth|under attack]] from [[Retriever Sentinel]]s from the Ark. A joint UNSC-[[Swords of Sanghelios]] [[Operation: FAR STORM|mission]] was launched to the Ark where it was discovered that the Ark's now-[[rampancy|rampant]] [[monitor]], [[000 Tragic Solitude]], had initiated the activation with the help of [[Bobby Kodiak]]. Having witnessed the destruction sentient life caused, particularly to Forerunner constructs, Tragic Solitude had activated the Array for a two-fold reason: to trick humanity into reactivating the portal so he could strip-mine Earth for materials to repair the Ark and eliminate the sentient species of the galaxy. Mann was able to deactivate the Array from the Ark and the team forced Tragic Solitude to end the Invasion of Earth. After Tragic Solitude attacked again, he was destroyed by Bobby Kodiak at the cost of his own life, ending the threat the rogue monitor posed to sentient life.{{Ref/Novel|HitD}} At some point following the loss of Installation 08, Installation 00 began to construct [[Installation 09|a new replacement]], one that would be maintained in the Ark's Foundry in a near-finished state for some time.{{Ref/Level|Id=Hold the Line|HW2|[[Hold the Line]]}}

In [[2556#February|February 2556]], the [[Outer Colony]] world of [[Sedra]] suffered a deadly [[bioweapon]] [[Terrorist attack on Sedra City|attack]] by [[Unidentified Sangheili Zealot (Sedra)|a Sangheili terrorist]]. The bioweapon source was traced to a new element mined from [[Alpha Shard|a surviving fragment]] of [[Installation 04]], created by the [[supernova]]-level explosion that had destroyed the original installation. A joint [[ONI]]-[[Sedran Colonial Guard]] [[Mission to Alpha Shard|mission]] was launched to capture the human smugglers mining the element and to destroy the deposits to prevent future use of the bioweapon. Though most of the team was killed, ONI [[Lieutenant Commander]] [[Jameson Locke]] and Sedran Private [[Talitha Macer]] escaped in the smugglers' {{Class|Bactrian|freighter}} while [[Colonel]] [[Randall Aiken]] sacrificed himself to destroy the deposits and the fragment's resident [[Lekgolo]] population with a [[HAVOK tactical nuclear weapon]].{{Ref/Film|HN}}

By early [[2557]], humanity had returned to the Ark and set up the [[Henry Lamb Research Outpost]]. Under the guidance of the [[smart AI]] [[Isabel]], the researchers began directing Retriever Sentinels to strip-mine lifeless systems to repair the Ark. The reconstruction slowly reached full automation until the humans were no longer needed to nudge it along. Over time, the Ark was repaired with noticeable differences between one day and the next over only the course of three months.{{Ref/Game|HW|Detail=''[[Phoenix Logs]]''}}

Later, the scientists studying Installation 03 located the [[Composer]] on the ring and accidentally activated it, causing them to [[mind transfer|become digitized]]. However, the sensor data left over from the incident led to the discovery of the [[shield world]] [[Requiem]]. Later, the [[Ur-Didact|Didact]] traveled to Ivanoff Station near Installation 03 to retrieve the Composer and used the device to harvest the essences of the entire research staff before heading for Earth.{{Ref/Game|H4}} Meanwhile, [[Jul 'Mdama's Covenant]] and their [[Promethean]] allies attempted to take control of Installation 03 by using the [[Conduit]] to open [[slipspace portal]]s across the ring, but the attack was repelled by a [[Spartan]] [[Headhunter]].{{Ref/Level|SS|[[Operation C: Valiant Hammer]]}}

[[File:HW2 I04C.png|thumb|250px|left|The [[Installation 09|second replacement Halo]] above the Ark in [[2559]].]]
A day later, after the Didact's [[New Phoenix Incident|defeat at Earth]], the Forerunner and some of his Promethean forces fell on Installation 03 via a slipspace portal. SPARTAN-II [[Blue Team]] followed, resulting in a [[Skirmish on Installation 03|a skirmish]] fought on both Installation 03 and the [[Composer's Forge]]. The Forge's monitor, [[859 Static Carillon]], transported Installation 03 over the Forge for the Didact, who intended to use the ring to finally destroy humanity.{{Ref/Comic|Id=HE9|HE|Detail=''[[Halo: Escalation Issue 9|Issue 9]]''}} However, the monitor instead allied with the Spartans due to his disagreements with the Didact and helped them defeat the Forerunner. After John-117 disabled the Halo's failsafes, Static Carillon ejected the segment housing the [[Control Room (Installation 03)|control room]], causing it to fall upon the Composer's Forge. The monitor then stabilized the ring and took it to an unknown location for repairs.{{Ref/Comic|Id=HE10|HE|Detail=''[[Halo: Escalation Issue 10|Issue 10]]''}}

In late [[2558]], Installation 00 became a battlefield once again as the mercenary organization known as the [[Banished]] arrived there following a sudden shutdown of the Earth portal. The Banished launched an assault on the UNSC bases on the Ark and soon gained control of the entire installation. In [[2559|May 2559]], the {{UNSCShip|Spirit of Fire}}, having drifted in space for 28 years, was mysteriously transported to Installation 00 by an agency evidently within the Ark.{{Ref/Level|HW2|[[The Signal]]}} During [[Second Ark Conflict|the ensuing conflict]] between the UNSC and the occupying Banished forces, Professor [[Ellen Anders]] learned of the contingency ring held within the Foundry and was able to launch the new Halo, with the intent of deploying it to Installation 04's former site in the [[Soell system]] where a [[distress beacon]] could be raised to the UNSC.{{Ref/Reuse|Hold the Line}} While the Halo was successfully sent through the portal, its firing mechanism disabled by Professor Anders, the ring was intercepted and forced out of slipspace on the way by a [[Guardian]].{{Ref/Level|Id=Last Stand|HW2|[[Last Stand (Halo Wars 2 level)|Last Stand]]}}

In October 2559, the Banished succeeded in opening a slipspace portal to [[Reach]] through which Atriox and some of his forces returned to the Milky Way galaxy in a [[Eklon'Dal Workshop Lich]]. Before the portal was shut down, [[Castor]] and the [[Keepers of the One Freedom]] hijacked Atriox's Lich and used it to fly back through the portal to the Ark, intending on using the Ark to fire the Halo Array and start the Great Journey.{{Ref/Novel|Id=SoR|SoR}} On the Ark, the Keepers allied themselves with [[Prelate]] [[Dhas Bhasvod]] and his [[Covenant loyalists]], guided by the Forerunner [[archeon-class ancilla]] [[Intrepid Eye]] who sought to fire the Halo Array in order to destroy the [[Domain]] and defeat [[Cortana]] for the sake of her own plans. The combined factions were opposed by both forces from the ''Spirit of Fire'' and the Banished spearheaded by the [[Clan of the Long Shields]] as neither the Banished nor the UNSC wanted Castor and Bhasvod to succeed. The Covenant and Keeper forces were able to reach [[Epsilon Clarion]], the only facility on the Ark capable of firing the Halo Array that was not inaccessible or inoperable. However, they suffered heavy casualties from UNSC and Banished [[Battle of Epsilon Clarion|attacks]] along the way and Castor abandoned his plans after learning the truth about the true purpose of Halo. On the order of [[Veta Lopis]], the ''Spirit of Fire'' launched an [[orbital bombardment]] of [[EMP]] [[MAC]] rounds that destroyed Epsilon Clarion and with it, Intrepid Eye and the Ark's ability to fire the Array. The Keepers were left decimated with only Castor and Sangheili [[Blademaster]] [[Inslaan 'Gadogai]] surviving while Bhasvod, after killing [[Mark-G313]], departed to link up with the rest of his own forces.{{Ref/Novel|Id=DW|DW}}

In [[2559#December|December 2559]], the Banished took over Installation 07 in search of the [[Xalanyn]] who had been imprisoned on the ring following the [[Great Purification]]. When the UNSC came to the ring in order to stop [[Cortana]] once and for all, [[Battle for Zeta Halo|a conflict]] erupted on the ring between the two sides, leading to the apparent destruction of the ''Infinity''. In [[2560#May|May 2560]], the [[Harbinger]] succeeded in locating her species just before the Master Chief killed her. Subsequently, Atriox reached and unlocked a facility on Zeta Halo holding the [[cylix]]es of the Xalanyn.{{Ref/Game|Hi}}

{{Clear}}

==Features==
[[File:LoreStream Halo Scale Comparison.png|left|thumb|250px|A scale comparison of the UNSC ''Infinity'' Mt. Rainier and a Halo Ring.]]
===Structure===
[[File:HaloLatticework.jpg|thumb|250px|The foundational latticework of a Halo installation.]]
The Halos encountered in the modern times are 10,000 kilometers in diameter; this size is roughly similar to that of [[Earth]], which is 12,756&nbsp;km in diameter. While the original twelve Halos had a diameter of 30,000 kilometers,<ref>'''Halo: Cryptum''', ''page 310''</ref> concerns about their structural stability and transport led to the second series of rings being reduced in size.{{Ref/Reuse|maker}} The surface of each ring is 318 kilometers wide,<ref>'''Halo: The Essential Visual Guide''', ''page 6''</ref> with a depth of 22.3 kilometers<ref>'''Halo: The Fall of Reach''', ''page 339'' (2001)</ref><ref>'''Halo: The Flood''', ''page 13'' (2003)</ref> to 47 kilometers.{{Ref/Reuse|Lorestream}}{{Ref/Note|The depth laid out in ''Halo: The Fall of Reach'' lists the ring's thickness as 22.3km, while the Lore Stream conducted by 343 Industries lists a depth of 47km. It is possible this disrepancy comes from the inclusion (or lack thereof) of the outer walls keeping the atmosphere in.}} The overall circumference of the ring is 31,415&nbsp;km and the interior surface area is 9,985,200&nbsp;km<sup>2</sup> - roughly the size of Canada.{{Ref/Reuse|Lorestream}} The main structure of the ring is constructed of a superdense foundational material,<ref>'''Halo: The Flood''', ''page 340''</ref> with elaborate scaffolding and cantilever structures laid over it to support the artificial landmasses and the myriad tunnel networks and caverns that riddle the installation's internal structure.{{Ref/Reuse|halo3halo}} Many of these tunnels are transit conduits meant for use by the ring's Sentinels, though some of them can be traversed by humanoid beings.<ref>'''[[Halo: Combat Evolved]]''', campaign level ''[[Halo (Halo: Combat Evolved level)|Halo]]''</ref>

The Halo rings achieve their "gravity" through [[artificial gravity]] generators - despite their shape, the ring does not need to spin to create its gravitational pull, though they do spin for other reasons unrelated to gravity generation.{{Ref/Reuse|Lorestream}} Due to this, the various [[Refugia]] present on the installation's surface may have different surface gravity, terrain, lighting and atmospheric conditions. These refugia are very modular and reconfigurable to support various types of life that are seeded on the rings.{{Ref/Reuse|Lorestream}} When the {{UNSCShip|Pillar of Autumn}} was detonated, it blasted a large mass from Installation 04; no longer a full loop, the centripetal force applied in much greater strength on the newly formed weak point, causing the ring to rip apart.<ref>'''Halo: Combat Evolved''' campaign level, ''[[The Maw]]''</ref>

[[File:HW2-Banished ejected.png|thumb|left|250px|A section of landmass being ejected from [[Installation 09]].]]
The Halos are capable of repairing themselves to some degree, replacing damaged plates of foundation material and restoring biological sections.<ref>'''Halo: Primordium''', ''page 77-78''</ref> Some of the 30,000&nbsp;km-diameter Halos could also be reduced to a smaller size by shedding large portions of the foundation.{{Ref/Reuse|maker}} In order to prevent the ring from falling apart during this process, it could generate a hard light hub with spokes which hold each of the foundation plates in place.<ref>'''Halo: Primordium''', ''pages 345-346''</ref> However, the self-reduction process was far from perfect and made the original Halos prone to instability and collapse.{{Ref/Reuse|maker}} The newer Halos are capable of safely ejecting segments as well due to their modular and reconfigurable construction,{{Ref/Reuse|Lorestream}} as long as the process is overseen by a capable enough intelligence such as a [[monitor]].{{Ref/Reuse|HE10}} Additionally, small, specifically defined parts of the Halos' terrain (along with the underlying foundation layers) can be jettisoned into space as a precautionary measure against Flood outbreaks.{{Ref/Reuse|Last Stand}}<ref name="cea t4">'''Halo: Combat Evolved Anniversary''', ''[[Terminal (Halo: Combat Evolved Anniversary)|Terminal Four]]''</ref> In time, the ecosystems of these ejected sections can be restored by the Halos' automated systems.{{Ref/Reuse|cea t4}}

Halos also possess [[hard light]] reinforcement to stabilize and protect them against tidal and gravitational forces from other objects.<ref>'''Halo: Cryptum''', ''page 311''</ref> One of the most extraordinary systems possessed by the Halos (at least the twelve original rings) is their ability to lock entire sections of the ring, or, if necessary, the entirety of it, into [[Slipspace bubble|reflective slipspace stasis]]. This suspends these sections in time and renders them invulnerable to damage from the outside, but consumes an enormous amount of energy.<ref>'''Halo: Primordium''', ''page 331-332''</ref>

Each installation in the final Halo Array orbits a large, dense planet—most commonly a gas giant—which serves as a gravitational anchor.{{Ref/Reuse|gas giants}}{{Ref/Reuse|Lorestream}} For example, Installation 04 and Installation 05 orbited [[Threshold]] and [[Substance]], respectively, which are both large gas giants, while Installation 03 is anchored to a large rocky planet.{{Ref/Reuse|h4composer}}
{{Clear}}

===Custodial===
[[File:343.JPG|right|thumb|250px|343 Guilty Spark, monitor of Installation 04.]]
The installations are designed to be run by advanced artificial intelligence constructs specially assigned by the Forerunners. The highest intelligence on each installation is a single monitor.<ref>'''Halo: Combat Evolved''', level ''[[343 Guilty Spark (level)|343 Guilty Spark]]''</ref> The monitor's task is to ensure that the installation's [[Sentinel]]s, which range from [[Constructor]]s to [[Sentinel Aggressor|Aggressors]] and [[Enforcer]]s, repair, maintain, and defend the ring from damage, contain Flood specimens, and ensure that their own installation is ready to fire on demand, including running activation simulations.{{Ref/Reuse|gravemind}} In the event that a Halo Ring is destroyed, Tragic Solitude, Custodian of Installation 00 had the authority to assign a monitor to a ring. However, because Tragic Solitude was destroyed, Installation 09 was not assigned a monitor to oversee it.{{Ref/Reuse|Lorestream}} Monitors also have access to their respective installation's defensive system.<ref>'''Halo: Combat Evolved Anniversary''', ''Terminal 1''</ref> Monitors are also permitted to make alterations to the Halo ring, as seen with 343 Guilty Spark ejecting sections of the ring during his time on Installation 04, as long as they do not interfere with primary functions of firing the Halo. Another instance of alterations made was with Installation 08, which would not be identical in every physical characteristic to Installation 04, as 343 Guilty Spark had made modifications and changes to the ring prior to its activation.{{Ref/Reuse|Lorestream}}

The Sentinels encompass a broad category of less intelligent constructs which serve virtually any purpose necessary to ensure that the Halo functions properly and are capable of combating small Flood outbreaks. Should a major Flood outbreak occur, heavier automatons, such as the Enforcers and [[Sentinel Major]]s will be created. In the meantime, Constructors are also created to ensure that the Forerunner structures on the Installation are kept in optimal shape, and that they are not damaged by conflict or weather.<ref name="Icon">'''Halo 2''', level ''[[Sacred Icon]]''</ref>

Save for the monitor, all automatons can be constructed at specialized [[Sentinel manufacturing facility|production facilities]] that float high in the Halo's atmosphere. They seem to have access to copious amounts of materials for constructing an almost indefinite number of automatons.

===Environment===
[[File:H2ABridge.jpg|thumb|left|250px|An environment on [[Installation 05]].]]
Although first and foremost designed as weapons of mass destruction, the Halos are also designed as habitats for transplanted lifeforms, including but not limited to humans. After [[Master Builder]] [[Faber]]'s plans were co-opted by the [[Librarian]], the Halos were given terrestrial surfaces to support cataloged specimens. The Master Builder intended to allow these specimens to be infected by Flood forms contained on the rings, and then subsequently terminated in order to test the Halos' effectiveness.{{Ref/Reuse|c313}} The Halo installations support a wide range of environments, habitats, ecosystems, and climates. Installation 04 and Installation 05 supported warm, temperate forests<ref>'''Halo 2''', level ''[[Uprising]]''</ref> that were both deciduous and coniferous, swamps, and cold, snow covered tundra environments.<ref>'''Halo: Combat Evolved''', level ''[[Assault on the Control Room]]''</ref><ref>'''Halo 2''', level ''[[Quarantine Zone]]''</ref>  Installation 00 had climate ranging all the way from tundra,<ref name="Cov">'''Halo 3''', level ''[[The Covenant (level)|The Covenant]]''</ref> to forest,{{Ref/Reuse|Cov}} to desert.<ref>'''Halo 3''', level ''[[The Ark (level)|The Ark]]''</ref>

While the terrain of a Halo ring may appear to be naturally formed at first glance, it is actually artificially constructed. [[Strato-Sentinel]]s extract raw materials from the source, process them in transit, and deposit building materials at the Installation.<ref>'''[[The Art of Halo 3]]''', page 30</ref> Four huge terraforming factories then move across the face of the installation to "skin" it with landmasses and bodies of water. These factories also hold in the ring's nitrogen-oxygen atmosphere, which is then leaked out to the surface, eventually pouring through the superstructure, and tugged in place by centripetal force;<ref>'''The Art of Halo 3''', ''page 116''</ref> massive walls lining both sides of the ringworld prevent the atmosphere from leaking out into space.<ref>'''Halo: Primordium''', ''pages 40, 148''</ref> 

An intricate layer of metallic panels is laid down several meters below the surface of the terrain, upon which rock, soil, and eventually vegetation is added. Slopes, hills and mountains can be created by sculpting these panels.{{Ref/Reuse|halo3halo}} Some features, such as landslides, are the result of time, and have been formed naturally. Others, such as the frigid conditions of the [[Quarantine Zone]] or the lake near the [[Temple (Installation 05)|Temple]] on [[Installation 05]] were artificially created.<ref>'''Halo 2''', campaign level ''[[Delta Halo]]''</ref> There are also numerous indigenous life-forms that live on the Halos; these were brought on the installations as part of the Lifeworkers' conservation project. The structures seen on the surface of the installations are built as part of the underlying structure, with the terrain then "printed" on top of them, creating the appearance of structures built into the surrounding landscape when the inverse is in fact true.{{Ref/Reuse|Lorestream}}
{{Clear}}
===Facilities===
[[File:AnniversaryControlRoom.png|thumb|right|250px|The [[Control Room]] of Installation 04.]]
Each Halo has several assets that are uniform to all installations. Each contains a [[control room]] located somewhere upon its inner surface. The control room houses the installation's mainframe, known as [[the Core]], from which all of the Halo's systems can be operated. The Halo's main weapon can be activated inserting the [[Activation Index]] into the Core; on the other hand, the Core may also be used to disable the main weapon.{{Ref/Reuse|Last Stand}} Each Halo also possesses a [[Library]], a large structure protected by [[Containment shield|an energy shield]] and a [[Sentinel wall|massive wall]], where the Index is housed and protected by Sentinels.{{Ref/Reuse|library}}{{Ref/Reuse|Icon}} The index itself is a semisolid [[holography|holographic]] representation of the data needed to activate the ring, and can only be directly inserted successfully by a Reclaimer.

Installations also possess [[Cartographer]] facilities, which contain the complete, real-time record and schematic of the installation,<ref>'''Halo: Primordium''', ''page 295''</ref> including its inner passages and networks, to be used as a navigational reference for traversing the installation. [[Flood containment facility|Flood containment]] and [[Flood research facility|research facilities]] are also standard, used by the installation's monitor to conduct research on and observe the surviving Flood specimens; these are protected by Sentinels to prevent an outbreak.<ref name="Flood240">'''Halo: The Flood''', pages 240-242</ref>

===Transportation===
[[File:HW2-Halo in slipspace.jpg|thumb|left|250px|Installation 09 exiting slipspace transit.]]
Facilities of the Halo Array contain advanced [[teleportation grid]]s, allowing instantaneous transportation for a Monitor or Reclaimer to any place on the installation. Under normal circumstances, these grids cannot be accessed by the Flood, though the Gravemind was able to use that of Installation 05 by controlling [[2401 Penitent Tangent]].{{Ref/Reuse|gravemind}} For Sentinels, the installation is riddled with tunnel and cave networks for access and transportation.{{Ref/Reuse|Flood240}} Teleportation grids make use of unmediated slipspace cores bound to them that generate stable, pre-computed slipspace routes between synchronised endpoints. Due to the fact that these devices have fixed endpoints (such as across an installation or its immediate vicinity), destination flexibility is sacrificed for safety, speed, and security.<ref name="WF11">''Halo: Warfleet'', p.11</ref>{{Ref/Reuse|gravemind}}

The Halo installations are also equipped with drive engines spaced along their rim.{{Ref/Reuse|Lorestream}} In the event of an emergency, a Halo can maneuver itself to avoid damage from a collision or weaponry.<ref>'''Halo: Cryptum,''', ''page 314''</ref> While ideally moved through fixed [[slipspace portal|portals]], the rings are able to perform slipspace jumps under their own power. In the case of at least the original twelve rings, a failsafe measure implemented in the event of capture by hostile forces would transition the Halo into slipspace and place it on a collision course with a planet or other celestial body, ensuring the weapon's destruction rather than allowing it to fall in the wrong hands.<ref>'''Halo: Primordium''', ''pages 279, 339''</ref> At the moment of [[Installation 04]]'s destruction, at least [[Alpha Shard|one major fragment]] of the ring was moved into slipspace, likely as part of a similar failsafe.<ref name="wp shard">[https://www.halowaypoint.com/en-us/universe/locations/halo-ring-fragment '''Halo Waypoint''': ''Alpha Shard'']</ref>
{{Clear}}

===Firing method===
[[File:H2A - Battle of Delta Halo.jpg|thumb|250px|left|Installation 05 as it aborts its firing sequence during the [[Battle of Installation 05]].]]
The seven installations in the final Halo Array function via form of lethal [[radiation]] designed to kill all [[sentience|sentient]] life in the installation's three-dimensional radius of 25,000 light-years; when fired in concert with the rest of the Array, this sterilizing effect covers the entire galaxy.<ref name="ENC">'''[[Halo Encyclopedia (2009 edition)]]''', ''pages 170-174''</ref><ref name="terminal8">'''Halo: Combat Evolved Anniversary''', ''[[Terminal (Halo: Combat Evolved Anniversary)|Terminal Eight]]''</ref>

When activated, the Halo rings release a burst of cross-phased supermassive neutrinos.{{Ref/Reuse|c274}} The burst possesses a harmonic frequency, which can be tuned to destroy the nervous system of any macroscopic organism that possesses one, even one as rudimentary as a notochord, as shown in the aftermath of a low-powered test firing of a Halo performed by [[Mendicant Bias]] in [[Charum Hakkor system|the system]] of Charum Hakkor. Fine tuning the pulse can also allow for selective extermination of lifeforms with varying degrees of neural complexity.<ref>[https://twitter.com/GrimBrotherOne/status/766840297498157056 '''Twitter''': ''Jeff Easterling on Twitter'']</ref> The Halo effect is able to target and eliminate most forms of neural structures, from biological nervous systems to esoteric [[neural physics]] constructs, although the effect does not extend to [[artificial intelligence]]s.<ref>'''Halo: Silentium''', ''page 310''</ref> It has been noted that neoteric array is capable of killing life with the neurological complexity above that of a bumblebee approximately.{{Ref/Reuse|Lorestream}} Simpler life forms that do not possess a neural system, such as microbes, fungi, algae, mosses, and traditional plants are unaffected.<ref name="c131">'''Halo: Cryptum''', ''pages 131-133''</ref> While organisms aboard the twelve older rings were safe from the Halo effect itself due to its directional nature, any sentient being would still experience an uncomfortable sensation in the vicinity of the pulse.<ref>'''Halo: Silentium''', ''pages 272-273''</ref> The semi-directional pulse of the senescent rings allowed for localised cleansing of star systems and clusters.{{Ref/Reuse|Lorestream}} Any living creature on the newer seven rings, however, would be killed and need to be reintroduced following the firing of the array. Furthermore, a key difference in the firing of the senescent and neoteric array is that the latter targets higher orders of life that are more complex neurologically, whereas the former will target and kill all life, which would lead to a complete collapse of planetary ecosystems as even insects are targeted. {{Ref/Reuse|Lorestream}}

Like virtually all Forerunner technology, the Halos are powered by [[vacuum energy]]. When the main weapon is fired, vacuum energy is siphoned from local space-time to near-depletion.{{Ref/Reuse|s270}} The pulse of the main weapon is amplified by a series of [[phase pulse generator]]s and channeled toward the Halo's center. A concentration of energy collects into the hub of the installation, which, when the weapon is fully charged, blasts outward in all directions.{{Ref/Reuse|terminal8}}

The radiation is propelled at superluminal speeds and will eventually propagate at a near-infinite velocity. This was known to generate causal paradoxes when the rings first fired, with two of the Halos reporting pre-echoes of the combined activation ''before'' the rings had been fired.{{Ref/Reuse|sil326}} Once activated from Installation 00, all installations will cumulatively trigger one another as their radiation fields intersect, amplifying the effects of each individual Halo.{{Ref/Reuse|s312}} The energy discharge covers the Array's effective range and cleanses it of all affected sentient life.{{Ref/Reuse|terminal8}} Individual Halos can also be fired independently from the rest of the Array; this is known as a "tactical pulse".{{Ref/Reuse|thecovenant}}

In the event a Halo's activation is canceled, a burst of energy is fired from the control center into the hub, causing the energy collected there to violently implode, then dissipate harmlessly.{{Ref/Reuse|great journey}}

The final Halo Array, comprising the six smaller Halos (and the reduced Installation 07) were designed to fire in all directions, within a spherical radius of 25,000 light-years;{{Ref/Reuse|radius}} together, the rings were capable of killing all sentient life within three radii of the Milky Way's center.{{Ref/Reuse|radius}} The original twelve Halos were designed to fire laterally, generating a cone-shaped field with a maximum effective range of hundreds of thousands light-years. When fired from the greater Ark to the [[Path Kethona|Large Magellanic Cloud]], the blast was wide enough to cover the entire 14,000 light-year-wide satellite galaxy.{{Ref/Reuse|s273}} The rings could also be fired on a lower power setting, cleansing specific planets or systems within a relatively small area of effect.{{Ref/Reuse|c131}}

===Effects===
[[File:Killed by Halo Effect.jpg|thumb|250px|A creature is killed by the activation of the Halo Array and is instantly decayed by the Lifeworker solvent.]]
The nervous systems of all beings are targeted by the Halos and destroyed, rendering them useless to the Flood; however, the Halo effect does not disintegrate biomass, leaving the victims' bodies mostly intact.<ref>'''Halo 3''', ''Terminal 6'' (''"I toss around [37,654 tonne] dreadnoughts like they were fighters; dimly aware of the former crews being crushed to liquescence."'')</ref> Left untreated, lifeforms killed by the pulse will decay in great masses, which could lead to ecological devastation spread by a miasma of rotten biomatter. Therefore, [[Lifeworker]]s sprayed target biospheres with a [[solute]] that would cause any animal killed by the Array to instantly decay into its component molecules,<ref>'''Halo: Silentium''', ''String Two''</ref> resulting in flash-desiccation.{{Ref/Reuse|terminal8}} Due to the Forerunners' use of solute, 21st century paleo-archeological studies gave no indication of the mass extinction caused by the Array's firing. However, in [[2332]] the [[Ross-Ziegler Blip]] revealed a tiny aberration in Earth's fossil records.<ref>'''Halo: Evolutions - Essential Tales of the Halo Universe''', ''"From the Office of Dr. William Arthur Iqbal"'', ''page 519''</ref>

The only known ways to avoid the effects of the pulse are to seek shelter in a [[shield world]] or to escape outside the range of the Array.{{Ref/Reuse|great journey}} However, the effects can be nullified by using a ring in an incomplete state. When [[Installation 08]] was fired in an incomplete state, [[John-117]] survived aboard the {{UNSCShip|Forward Unto Dawn}}, the Covenant Loyalists survived aboard [[Anodyne Spirit]], and native animals on Installation 00 also survived the firing. Flood aboard [[High Charity]] also survived the firing, but [[Installation 00]]'s Sentinels were able to contain those that survived with a [[containment shield]] around the ruined structure.

Halo Installations make use of [[Composer]] technology to an unknown degree as part of their firing.{{Ref/Reuse|Lorestream}}

===Protocol===
{{Main|Containment protocol}}
Each Halo ring can be activated individually by a [[Reclaimer]], also placing the other installations in standby mode, or they can all be activated simultaneously from Installation 00. In the event of a major Flood outbreak, an installation's monitor will seek out a Reclaimer if available, whom they will enlist to aid them. It will [[Slipspace translocation|teleport]] them to the installation's Library and will assist the individual in retrieving the Index. The monitor then stores the Index within its data arrays for safe transportation, lest the Reclaimer fall prey to the Flood before they can activate the installation. Once at the control room, the Reclaimer is given back the Index and must insert it into [[the Core]] in order to begin the activation sequence. At any point during the charging sequence, a Reclaimer is able to abort the firing by removing the Index from the Core.{{Ref/Reuse|great journey}}

===Defenses===
Each Halo ring has its own defenses, though Sentinels from Installation 00 are always deployed at a newly constructed ring to finalize preparations to launch it. [[Retriever Sentinel]]s are also stored inside the rings and will deploy automatically to attack anything deemed a threat.<ref>''Halo Wars 2'', campaign level, ''[[The Halo]]''</ref> The threat of the Sentinel defenses of Installation 03 were cause for [[Ivanoff Station]] to keep a permanent complement of [[F-41 Broadsword|Broadsword]] fighters and [[Mark 2551 Onager]] defense cannons on hand at all times, to ensure the station's defense.<ref name="ivanoff">'''[[Halo: Warfleet – An Illustrated Guide to the Spacecraft of Halo|Halo: Warfleet]]''', ''Space Stations'', ''pages 34-35''</ref> The exterior band of Halo installations contains a series of [[Confidence-class weapon array|''Confidence''-class weapon arrays]], which can be used to enforce an exclusion zone of up to one light-year. UNSC ''Pillar of Autumn'' was initially tagged as a hostile by 343 Guilty Spark using Installation 04's ''Confidence''-class defense system, but was given clearance after scans revealed that humans were aboard.<ref name="lorestream">[https://www.youtube.com/watch?v=fYaxRoAf96s '''YouTube:''' ''Halo Lore Stream: The Halo Array'']</ref><ref name="CEATerminal1">[[Halo: Combat Evolved Anniversary Terminals]]</ref> 
{{clear}}

==List of installations==

===Prototypes===
{| class="wikitable" style="width:100%; border:1px solid #999999; background: #FFFFFF;"
! style="width:100px;" | Name
! style="width:100px;" | Location
! style="width:100px;" | Monitor
! style="width:100px;" | Status
|-
|[[Prototype Halo installation|Miniature Halo installation]]
|Hidden sector of the galaxy in orbit of a rogue planet
|None
|Destroyed
|}

===Senescent Array===
{| class="wikitable" style="width:100%; border:1px solid #999999; background: #FFFFFF;"
! style="width:100px;" | Name
! style="width:100px;" | Location
! style="width:100px;" | Monitor
! style="width:100px;" | Status
|-
|[[Greater Ark]]
|Extragalactic space
|[[Offensive Bias]]
|Destroyed
|-
|[[Omega Halo]]/Gyre 09
|Orbiting the greater Ark
|N/A
|Destroyed
|-
|Gyre 11
|N/A
|N/A
|Changed into [[Installation 07]]
|-
|}

===Neoteric Array===
The installations in the neoteric{{Ref/Reuse|neoteric}} Halo Array are numbered in the order they were built in,{{Ref/Reuse|neoteric}} while their alphabetical designations were assigned in the order in which they were fired, with [[Installation 04|Alpha Halo]] being the first ring to fire.<ref>''Halo: Silentium'', p. 327</ref> Although [[Installation 07]] was originally constructed as part of the first series of larger Halos, it was the last ring to be added to the neoteric Array while being heavily modified to suit its new role, hence the designation.<ref>[https://www.reddit.com/r/halo/comments/70wbxc/return_to_the_denomination_installation_04_b_c/dn76qup/ ''Reddit: Return to the denomination. Installation 04 (B), (C). Canonically. 343 PLS'' (comment by GrimBrotherOne)]</ref>

{| class="wikitable" style="width:100%; border:1px solid #999999; background: #FFFFFF;"
! style="width:100px;" | Designation
! style="width:100px;"  | Name
! style="width:200px;" | Location
! style="width:250px;" | Monitor
! style="width:250px;" | Status
|-
|[[Installation 00]]
|Lesser Ark
|[[Intergalactic space|Extragalactic space]]
|[[000 Tragic Solitude]] ''(destroyed)''
|Heavily damaged, then repaired; contested between the [[Banished]] and the {{UNSCShip|Spirit of Fire}}
|-
|[[Installation 01]]
|Beta Halo
|[[Auric]] orbit, [[Myung system]]{{Ref/Book|Id=enc22p345|Enc22|Page=345}}, [[Orion Arm]]<ref name="WarfleetGalaxy">''[[Halo: Warfleet]]'', p. 12-13</ref>
|[[001 Shamed Instrument]]
|Intact
|-
|[[Installation 02]]
|Epsilon Halo
|[[Taphro]] orbit, [[Zhagolin system]]{{Ref/Book|Id=enc22p347|Enc22|Page=347}}, [[Norma Arm]]{{Ref/Reuse|WarfleetGalaxy}}
|[[007 Contrite Witness]]
|Intact
|-
|[[Installation 03]]
|Gamma Halo
|[[Doavyn]] orbit, [[Khaphrae system]], [[Scutum-Centaurus Arm]]{{Ref/Reuse|WarfleetGalaxy}} {{C|formerly}}
|[[049 Abject Testament]] ''(missing)''
|Major surface damage; control room ejected and destroyed
|-
|[[Installation 04]]
|Alpha Halo
|[[Threshold]] orbit, [[Soell|Soell system]], [[Orion Arm]]{{Ref/Reuse|WarfleetGalaxy}}
|[[343 Guilty Spark]] ''(absent)''
|Destroyed; wreckage under [[Joint Occupation Zone|joint]] [[UNSC]]-[[Swords of Sanghelios]] quarantine per the [[Treaty of 2552]] preventing the return of either faction
|-
|[[Installation 05]]
|Delta Halo
|[[Substance]] orbit, [[Coelest system]], [[Norma Arm]]{{Ref/Reuse|WarfleetGalaxy}}
|[[2401 Penitent Tangent]]
|Surface [[Glassing|glassed]]; under joint UNSC-Swords of Sanghelios quarantine
|-
|[[Installation 06]]
|Kappa Halo
|[[Haakuth]] orbit, [[Mdorkon system]]{{Ref/Book|Id=enc22p349|Enc22|Page=349}}, [[Perseus Arm]]{{Ref/Reuse|WarfleetGalaxy}}
|[[16807 Abashed Eulogy]]
|Intact
|-
|[[Installation 07]]
|Zeta Halo<br>Gyre 11 {{C|Originally}}
|[[Ephsu I]] orbit, [[Ephsu system]], [[Sagittarius Arm]]{{Ref/Reuse|WarfleetGalaxy}} {{C|formerly}}
|[[117649 Despondent Pyre]] ''(destroyed)''<br>[[Adjutant Resolution]]
|Damaged, controlled by the Banished
|-
|}

======Replacements======
{| class="wikitable" style="width:100%; border:1px solid #999999; background: #FFFFFF;"
! style="width:100px;" | Designation
! style="width:50px;"  | Original
! style="width:100px;" | Name
! style="width:200px;" | Location
! style="width:100px;" | Monitor
! style="width:100px;" | Status
|-
|[[Installation 08]]<ref name="RedditGrim">[https://www.reddit.com/r/halo/comments/70wbxc/return_to_the_denomination_installation_04_b_c/dn6n4h7/ ''Reddit: Return to the denomination. Installation 04 (B), (C). Canonically. 343 PLS''] "Sorry, 08 and 09 make way more sense :-)
In actuality, they aren't meant to directly replace an individual ring, but to replace the loss in coverage that ring offered the galaxy.",
 [[Jeff Easterling]]</ref>
|Installation 04
|Alpha Halo (replacement)
|Destroyed Over Installation 00
|343 Guilty Spark ''(absent)''
|Destroyed
|-
|[[Installation 09]]{{Ref/Reuse|RedditGrim}}
|Installation 04
|Alpha Halo (replacement)
|Between Installation 00 and the Soell system
|None
|Controlled by the [[Created]]
|}

==Trivia==
{{Linkbox|gallery=yes|gallerypage=Images of Halos}}
*The Halos are remarkably similar to the eponymous megastructure of [[Wikipedia:Larry Niven|Larry Niven]]'s ''[[Wikipedia:Ringworld|Ringworld]]'' series. However, Niven's Ringworld encircles a large star, whereas the Halos merely orbit planets, being much smaller than the former. The Halos are also very similar to the [[Wikipedia:Orbital (The Culture)|Orbitals]] from [[Wikipedia:Iain M. Banks|Iain M. Banks']] ''Culture'' series, though considerably smaller.
*In a ''Halo: Combat Evolved'' [[Pre-Xbox Halo|prototype]], Installation 04 had a section that was only partially constructed. This feature was dropped from the final game, though it inspired the design of Installation 08.
*The Prophet of Mercy once referred to the Halo Array's pulse as a divine wind.{{Ref/Reuse|Icon}} This is a literal translation of ''[[Wikipedia:Kamikaze|kamikaze]]'', suicide attacks carried out by Japanese pilots against Allied vessels near the end of World War II. ''Kamikaze'' aviators were willing to give their lives based on their fanatical devotion to defend [[Wikipedia:Hirohito|Emperor Hirohito]] and the state. This is mirrored by the Covenant's quest to activate the Halos and commit holy war in deference to their gods.

== Gallery ==
<gallery>
File:HCE-AlphaHalo-SurfaceDetail.jpg|Installation 04 in ''[[Halo: Combat Evolved]]''.
File:Delta Halo.jpg|Installation 05 in ''[[Halo 2]]''.
File:H2_halo_surfaceland.jpg|The surface of a Halo ring.
File:Halo 3 - Installation04B.jpg|Installation 08 in ''[[Halo 3]]''.
File:HaloLegends-Origins-HaloArray.png|A Halo installation in ''[[Origins]]''.
File:Halo-Legends-Origins-1 HaloArrayFiring.jpg|A Halo being fired.
File:HaloLegends-Origins-HaloPostFiring.png|A Halo ring's pulse dimming after its activation.
File:TML - broken Halo.png|Broken Installation 04 in ''[[The Mona Lisa]]''.
File:LFA-43 Halo.png|Installation 04 in ''[[Halo: Combat Evolved Anniversary]]''.
File:FUD-HaloRing.jpg|A visual reference to a Halo ring in ''[[Halo 4: Forward Unto Dawn]]''.
File:H4-GammaHaloInst03-ScanScreen.jpg|Installation 03 in ''[[Halo 4]]''.
File:HE Installation 03.jpg|Installation 03 ejecting a section of itself in ''[[Halo: Escalation]]''.
File:HNF-Alpha Shard.jpg|Alpha Shard in ''[[Halo: Nightfall]]''.
File:H2A - ZenithRing.jpg|Installation 05 in ''[[Halo 2: Anniversary]]''.
File:Halo ring and thing.jpg|A post-war human [[space station|station]] near an unknown Halo installation in ''[[A Hero Falls]]''.
File:HSS-Gamma Halo Pelican.png|Installation 03 in ''[[Halo: Spartan Strike]]''.
File:H5G-LegendaryHalo.png|Installation 07 in ''[[Halo 5: Guardians]]''.
File:HM-Thanolekgolo.png|Alpha Shard in ''[[Halo Mythos]]''.
File:HW2-Halo.png|Captain [[James Cutter]] stands before Installation 09 in ''[[Halo Wars 2]]''.
File:MCC_Halo_Background.jpg|A Halo ring in the menu background of ''[[Halo: The Master Chief Collection]]''.
File:FH4 - Halo Showcase Skybox.png|''[[The Halo Experience Showcase]]''{{'}}s unique skybox featuring a Halo ring in ''Forza Horizon 4''.
File:HI E319 TheRingReveal.png|John-117 gazing at a destroyed Installation 07 from the ''[[Halo Infinite]] [[Discover Hope]]'' trailer.
File:HINF FullZetaHalo.png|Installation 07 as viewed by John-117 in space.
File:HINF DoisacHalo Concept.jpg|''Halo Infinite'' concept art of a Halo ring firing upon and destroying [[Doisac]].
</gallery>

==List of appearances==
{{Col-begin}}
{{Col-2}}
*''[[Halo: The Fall of Reach]]'' {{1st}}
*''[[Halo: Combat Evolved]]''
*''[[Halo: The Flood]]''
*''[[Halo: First Strike]]''
*''[[Halo 2]]''
*''[[Halo Graphic Novel]]''
**''[[The Last Voyage of the Infinite Succor]]''
*''[[Halo: Ghosts of Onyx]]''
*''[[Halo: Uprising]]'' {{Mo}}
*''[[Halo 3]]''
**''[[Bestiarum]]'' {{Mo}}
*''[[Halo: Contact Harvest]]'' {{Mo}}
*''[[Halo: The Cole Protocol]]'' {{Mo}}
*''[[Halo Wars]]'' {{Mo}}
*''[[Halo Legends]]''
**''[[Origins]]''
**''[[Homecoming]]''
**''[[Odd One Out]]'' {{C|Non-canonical appearance}}
*''[[Halo: Evolutions - Essential Tales of the Halo Universe]]''
**''[[The Mona Lisa]]''
*''[[Halo: Reach]]''
*''[[Halo: Cryptum]]''
*''[[Halo: Glasslands]]'' {{Mo}}
*''[[Halo: Combat Evolved Anniversary]]''
**''[[Terminal (Halo: Combat Evolved Anniversary)|Terminals]]''
*''[[Halo: Primordium]]''
*''[[Halo: The Thursday War]]'' {{Mo}}
*''[[Halo 4: Forward Unto Dawn]]'' {{C|Visual allusion}}
{{Col-2}}
*''[[Halo 4]]''
**''[[Terminal (Halo 4)|Terminals]]''
*''[[Halo: Silentium]]''
*''[[Halo: Escalation]]''
*''[[Halo: Broken Circle]]'' {{C|Holographic representation only}}
*''[[Halo: Nightfall]]''
*''[[Halo 2: Anniversary]]''
**''[[Terminal (Halo 2: Anniversary)|Terminals]]''
*''[[Halo: New Blood]]'' {{Mo}}
*''[[Halo: Hunters in the Dark]]''
*''[[Halo: Last Light]]'' {{Mo}}
*''[[Halo 5: Guardians A Hero Falls trailer|A Hero Falls]]''
*''[[Halo 5: Guardians]]''
*''[[Halo: Shadow of Intent]]'' {{Mo}}
*''[[Halo Mythos]]''
*''[[Halo: Fractures]]''
**''[[Promises to Keep]]'' {{Mo}}
**''[[Untitled story (Halo: Fractures)|Untitled story]]'' {{Mo}}
*''[[Halo Wars 2]]''
*''[[Halo: Envoy]]'' {{Mo}}
*''[[Halo: Retribution]]'' {{Mo}}
*''[[Halo: Legacy of Onyx]]'' {{Mo}}
*''[[Halo: Official Spartan Field Manual]]''
*''[[Halo: Renegades]]'' {{Mo}}
*''[[Halo: Outpost Discovery]]''
*''[[Halo: Shadows of Reach]]'' {{Mo}}
**''[[Sacrifice]]'' {{Mo}}
*''[[Halo: Point of Light]]''
*''[[Halo: Divine Wind]]'' {{Mo}}
*''[[Halo Infinite]]''
*''[[Halo: The Television Series]]''
**''[[Unbound]]'' {{Mo}}
**''[[Homecoming (TV Series)|Homecoming]]'' {{Mo}}
**''[[Solace (TV Series)|Solace]]''
**''[[Allegiance]]''
**''[[Transcendence]]''
*''[[Halo: The Rubicon Protocol]]''
{{Col-end}}

==Notes==
{{Ref/Notes}}

==Sources==
{{Ref/Sources|3}}

==See also==
*[[The Anatomy of Halo]]
*[https://www.youtube.com/watch?v=fYaxRoAf96s Halo Lore Stream: The Halo Array] - a lore stream conducted by [[Jeff Easterling]] and [[Kenneth Peters]], focusing on the Halo Array.
{{Forerunner|array}}

[[Category:Halo Array| ]]
[[Category:Forerunner weapons]]