Editing Installation 04

{{Status|Canon}}
{{Center|'''''Installation 04''' redirects here. For other uses, see [[Installation 04 (disambiguation)]]''.}}
{{Megastructure infobox
|image=[[File:H2A-AlphaHaloDiscovery.jpg|300px]]
|description=
|location=[[Soell|Soell system]], in orbit around [[Threshold]],{{Ref/Book|Id=VIS|EVG|Page=6}} [[Orion Arm]],{{Ref/Book|Id=warfleet|HWF|Page=12}} [[Milky Way]]
|anchor=Threshold/[[Basis]]{{Ref/Reuse|VIS}}
|type=[[Halo Array|Halo Installation]]
|function=*Galactic sterilization{{Ref/Site|Id=halo array|URL=https://www.halowaypoint.com/en-us/universe/tech/halo-array|Site=Halo Waypoint|Page=Halo Array|D=9|M=4|Y=2015}}
*[[Flood]] containment and research{{Ref/Reuse|halo array}}
|caretaker=[[Monitor]] [[343 Guilty Spark]]
|constructed=[[97,445 BCE]]{{Ref/Reuse|halo array}}
|destroyed=[[2552#September|September 22, 2552]]
|diameter={{Convert|10000|km|mi|sp=us|sigfig=4}}{{Ref/Reuse|VIS}}
|surface width={{Convert|318|km|mi|sp=us|sigfig=3}}{{Ref/Reuse|VIS}}
|gravity=0.992 G (approx){{Ref/Reuse|VIS}}
|surface temperature=-23°C to 40°C (-9°F to 104°F) (controlled){{Ref/Reuse|VIS}}
|atmosphere=1 ([[Wikipedia:Nitrogen|N<sub>2</sub>]], [[Oxygen|O<sub>2</sub>]]){{Ref/Reuse|VIS}}
}}
{{Quote|Whoever controls Halo controls the fate of the universe.|[[Captain (Navy)|Captain]] [[Jacob Keyes]]}}
'''Installation 04''', also known as '''Alpha Halo''', or simply '''Halo''',{{Ref/Level|CE|CE:The Truth and Reconciliation|Truth and Reconciliation|Quote=They call it, Halo.|Quotee=Jacob Keyes}} was one of [[seven]] ring-shaped superweapons that comprised the [[Forerunner]]s' [[Halo Array]]. It was located in the [[Soell system]] in the [[Orion Arm]] and was the closest Halo ring to the [[human sphere]].{{Ref/Reuse|warfleet}}

The [[Covenant]] reverentially described Installation 04 as either the '''First Holy Ring''' or the '''First Sacred Ring'''. After its destruction at the end of the [[Battle of Installation 04]], [[Installation 00|the Ark]] started to construct [[Installation 08|a replacement for Installation 04]]. After the replacement was destroyed, the Ark constructed [[Installation 09|yet another replacement]].

==Overview==
[[File:HCE-AlphaHalo-RingDetail.jpg|thumb|250px|right|Installation 04.]]

The purpose of Installation 04, along with its brethren, was to preclude and thwart the parasite forms known as the [[Flood]] from consuming all sentient life in the galaxy by destroying all sentient life to prevent eventual consumption. In the event of a Flood outbreak, one of the seven installations could be triggered (in turn triggering the remaining Halos) to annihilate all sentient life within a radius of 25,000 light years. In the event of an unexpected shutdown, all remaining rings would go into a "standby state", in which they could be fired at once from the Ark if need be.

Installation 04, until its destruction by John-117, was controlled by the [[Forerunner]] artificial intelligence construct ([[Monitor]]), [[343 Guilty Spark]].

===Astronomical Features===
Installation 04 orbited the massive gas giant [[Threshold]], and was suspended in the [[Lagrange point]] between Threshold and its largest [[natural satellite]], [[Basis]]. The installation had a 24-degree axial tilt from Threshold's orbital plane. Due to this, any given point on the surface of the ring received sunlight from the star [[Soell]] for half of the time it was on the sunny side of Threshold, and none when was on the dark side. This created a somewhat unusual day-night cycle for the ring, in which it was dark three-fourths of the time and had no sunrise or sunset similar to those of a planet.{{Ref/Book|Halo: Combat Evolved: Sybex Official Strategies & Secrets|Page=64}}

With a diameter of 10,000&nbsp;km and a surface width of 318&nbsp;km, the ring has a surface area of 9,990,000&nbsp;km<sup>2</sup>.

===Environmental Features===
The climate of Installation 04 was very similar to [[Earth]]'s climate. The weather was, however, extremely unpredictable - rain and snowfall could occur at random, leading [[Cortana]] to wonder if the weather was intentionally irregular, or if it followed a pattern, such as snow being deliberately triggered at the control room to slow the Flood.{{Ref/Novel|Id=TF4|TF|Chapter=4}}{{Ref/Level|Id=aotcr|CE|CE:Assault on the Control Room|Assault on the Control Room}} Rain was observed stopping as if at the flip of a switch.{{Ref/Novel|Id=flood5|TF|Chapter=5}} There have been hurricanes over the oceans on the ring.{{Ref/Novel|Id=TF1|TF|Chapter=1}} "Blood-warm" rain occurred during the [[UNSC]] occupation of [[Alpha Base (Installation 04)|Alpha Base]].{{Ref/Reuse|TF4}}

====Locations====
*[[Alpha Base (Installation 04)|Alpha Base]]
*"[[Battle Creek]]"
*[[CE:Halo|Beacon towers]]
*"[[Blood Gulch]]"
*"[[Chill Out]]"
*[[Control Room (Installation 04)|The Control Room]]
*"[[Damnation]]"
*[[Flood containment facility]]
*"[[Hang 'Em High]]"
*[[Library|CE:The Library|The Library]]
*"[[Longest]]"
*[[Phase pulse generator|Phase pulse generators]]
*[[CE:The Maw|''Pillar of Autumn'' crash site]]
*"[[Prisoner]]"
*"[[Rat Race]]"
*"[[Ridgeline]]"
*[[Sector 1215]]
*"[[Sidewinder]]"
*[[Silent Cartographer#Installation 04CE:The Silent Cartographer|The Silent Cartographer]]
*"[[Tempest]]"
*[[CE:The Truth and Reconciliation|''Truth and Reconciliation'']] [[Keyes|landing plateau]]
*[[Weather spire|Weather spires]]
*"[[Wizard]]"

[[File:HCE - Halo.jpg|thumb|200px|left|The surface of Installation 04.]]

===Ecology===
The ring boasted many diverse biomes and ecosystems across its habitable inner surface, including mountain ranges, glaciers, deserts, jungles, temperate forests, lush swamps, arid highlands, and vast seas.{{Ref/Reuse|TF1}} The area where Alpha Base was located was remarked as being comparable to the Cascade mountain range of Earth's Pacific Northwest.{{Ref/Novel|Id=flood7|TF|Chapter=7}}

====Flora====
{{quote|I'm reading thousands of types of flora. The ring's ecosystem is incredibly sophisticated.|[[Cortana]]}}
Multiple varieties of coniferous trees, broadleaf trees, ferns, clovers, low-growing bushes, [[Wikipedia:Xerophyte|xerophytic]] scrubs, and various grasses were a common sight in many of its biomes. Many species grew directly from cliff walls and elevated rock features. Aquatic plants could be found in some of its streams and rivers.{{Ref/Reuse|CEL2}} One tree species distributed across multiple biomes on the ring shared morphological similarities with Earth [[Wikipedia:Araucaria|Araucaria trees]], but with leaf architecture similar to fan palms; these were seen reaching massive size in the swamps around the [[Flood containment facility]].{{Ref/Level|Id=CEL2|CE|Halo (Halo: CE level)|Halo}}{{Ref/Level|Id=CEL4|CE|Silent Cartographer}}{{Ref/Level|Id=CEL6|CE|CE:343 Guilty Spark|343 Guilty Spark}}{{Ref/Reuse|CEA343}}

The area near the [[Beacon tower|beacon towers]] where Master Chief first made landfall had a striking similarity to the Pacific Northwest of [[Earth]]. The meadowed landscape featured many species of pine tree, including [[Douglas fir|Douglas firs]] and some trees resembling upright [[Wikipedia:Juniper|juniper]] or [[Wikipedia:Cypress|cypress]]. Hanging vines with a helical growth pattern were observed on the cliffs, alongside other species of ivy.{{Ref/Reuse|CEL2}}{{Ref/Level|Id=CEAHalo|CEA|Halo}}

One [[CE:The Truth and Reconciliation|plateau]] in an arid region on the ring showed extensive exposure of lateral root systems in its rock walls, in addition to various low-growing shrubs and juniper-like trees with a spiral trunk structure.{{Ref/Level|Id=CEATnR|CEA|CE:The Truth and Reconciliation|Truth and Reconciliation}}

The island housing the installation's [[Cartographer]] had trees with large buttressed aerial root structures similar to [[Wikipedia:Mangrove|mangroves]], suggesting the trees needed extra stability in soft soil. Plants very similar to [[Wikipedia:Bromeliaceae|bromeliads]] with [[Wikipedia: Epiphyte|epiphytic]] root mats could be found on the island. Large toadstools could be found on some trees around the island.{{Ref/Level|Id=CEASC|CEA|CE:The Silent Cartographer|The Silent Cartographer}}

Some of the ring's arctic regions featured very tall pine trees and small shrubs suited to the cold environment.{{Ref/Reuse|aotcr}}{{Ref/Level|Id=CEAaotcr|CEA|CE:Assault on the Control Room|Assault on the Control Room}}

[[File:HGN_LastVoyageSwamp.png|thumb|right|350px|A swamp on Installation 04.]]
The swamps around the [[Flood containment facility]] had extensive organic mats and humus covering much of its surface,{{Ref/Novel|Id=flood8|TF|Chapter=8}} sometimes growing around and subsuming structures which may have been decaying tree stumps, and hosted species of aquatic reeds, water lillies, fan palms, and multiple types of variegated [[Wikipedia:Tree fern|tree ferns]], one of which could be found at at least [[Blood Gulch|one other location]].{{Ref/Reuse|CEBGulch}} The swamp showcased some of the installation's exotic megaflora, including giant trees with thick, "spider-like" roots,{{Ref/Reuse|flood8}}, the shape of which may have been formed after the tree grew on decaying matter, which subsequently eroded. Their high crowns formed a canopy at a height of 76.8 meters, preventing most sunlight from reaching the ground. The swamp was also home to large, [[Swamp tree|bioluminescent fungi]] which grew up to a height of at least 40.5 meters. The same helical hanging vines near the beacon towers grew from the canopies and branches, along with the same species of bromeliad-like plants found on the Cartographer island. [[Wikipedia:Strangler fig|Stranglers]] could be seen encasing many of the trees, and uniquely large [[Wikipedia: Stromatolite|stromatolitic]] fungal growths with heights up to 4.4 meters and a diameter up to 8.9 meters were observed.{{Ref/Reuse|CEL6}}{{Ref/Reuse|CEA343}}

[[Ridgeline|One area]] of the ring also showed a similarity to Earth's Pacific Northwest, populated with pine and birch trees, ferns, and idyllic grassy reaches. It was home to numerous types of low-growing flowering plants reminiscent of [[Wikipedia:Lilium|lilly]], [[Wikipedia:Phlox|phlox]], and [[Wikipedia:Bellis perennis|daisies]].{{Ref/Reuse|HRRidge}}

The area around the [[Tempest|weather spires]] was also evocative of the Pacific Northwest, and had plants nearly identical to the [[Wikipedia:Eschscholzia californica|California poppy]].{{Ref/Reuse|HRTemp}}

Cryptogam growth could be observed on many architectural, geological, and organic structures (like tree trunks), including various types of moss, fungi, and lichen, some of which grew [[Wikipedia:Spanish moss|aerially]] or in large [[Wikipedia:Fruticose lichen|fruticose]] masses.{{Ref/Map|Id=CEBGulch|CE|Blood Gulch}} [[Wikipedia:Mycelium|Mycelial]] growth patterns could be seen with the naked eye in many patches of soil on the installation.

====Fauna====
On many regions of the ring, plentiful animal cries could be heard, some uncannily reminiscent of Earth natives such as songbirds, frogs,{{Ref/Reuse|CEA343}} [[Wikipedia:Peafowl|peafowl]],{{Ref/Reuse|CEL2}} and [[Wikipedia:Howler monkey|howler monkeys]].{{Ref/Level|Id=CEA343|CEA|343 Guilty Spark}} Insect noises similar to those produced by Earth crickets, cicadas, and flies could also be heard. Insect bite marks were observed on the leaves of various local flora.{{Ref/File|CE|D20.map\gbxmodel\scenery\plants\plant_yellowbig\plant_yellowbig.gbxmodel}} Plentiful aquatic life could be found in the waters around the [[Cartographer]] island, including crabs, [[Wikipedia:Crown-of-thorns starfish|Crown-of-thorns]]-like starfish, saltwater [[Wikipedia:Discus (fish)|discus fish]], [[Lumenon]],{{Ref/Level|CEV|CEV:The Silent Cartographer|The Silent Cartographer}} and [[Sea worm|Sea worms]].{{Ref/Reuse|CEL4}} The swamps around the [[Flood containment facility]] hosted species of moth-like insects, swamp birds,{{Ref/Reuse|flood8}} and fireflies.{{Ref/Reuse|CEL6}}  The area around the ring's [[Tempest|weather spires]] was home to [[Wikipedia:Bluegill|bluegill]], seagulls, and had berry-producing plants that were likely evidence of reproduction through [[Wikipedia:Seed dispersal syndrome#Zoochory|zoochory]].{{Ref/Map|Id=HRTemp|HR|Tempest}} [[Ridgeline|Another location]] was home to [[Wikipedia:Monarch butterfly|monarch butterflies]] and wildflowers, possibly indicating other pollinators.{{Ref/Map|Id=HRRidge|HR|Ridgeline}}

The ring's catalogued species included colonies of [[Thanolekgolo]].{{Ref/Film|Id=HNC3|Film=Halo: Nightfall|Episode=Lifeboat Rules|EpisodeLinkText=Chapter Three: Lifeboat Rules}}
 
{{col-begin}}
{{col-2}}
*[[Wikipedia:Bluegill|Bluegill]]
*Crabs
*[[Wikipedia:Crown-of-thorns starfish|Crown-of-thorns]]-like starfish
* Saltwater [[Wikipedia:Discus (fish)|discus fish]]
*Doves
*Fireflies
*[[Wikipedia:Gull|Gulls]]
*[[Lumenon]]
{{col-2}}
*[[Merse]]{{Ref/Generic|Id=HRLERM|Halo: Risk: Legendary Edition|The Ring Map}}
*[[Wikipedia:Monarch butterfly|Monarch butterfly]]
*Mosquitoes
*Moths
*''[[Olfmeri]]''{{Ref/Reuse|Id=HRLERM}}
*''[[Rangmejo]]''
*[[Sea worm]]
*''[[Zavfaraa]]''{{Ref/Site|Id=CFDigsite|URL=https://www.halowaypoint.com/news/canon-fodder-digsite-dissection|Site=Halo Waypoint|Page=Canon Fodder - Digsite Dissection|D=28|M=07|Y=2023}}
{{col-end}}

[[File:TML - broken Halo.png|thumb|left|250px|A segment of the broken ring.]]

====Destruction====
After the ring's [[Battle of Installation 04|destruction]], trees were observed floating on bits of detritus in its debris field.{{Ref/Film|Id=EvoTML|EvoMC|Story=The Mona Lisa}}

On the [[Alpha Shard]], extreme conditions caused by unstable proximity to [[Thotael system|Thotael]] only allowed extremophiles to survive the searing hot sixteen-hour "days", alongside organisms capable of seeking proper shelter. The extremophiles included moss-like vegetation, ferns, grasses, and small plants, all with coloration suggesting a [[Wikipedia:Chlorophyll|chlorophyllous]] process. [[Talitha Macer|Macer]] speculated the plant life surviving on the fragment possibly wasn't carbon-based, but [[Gregory Ramos|Ramos]] responded that it "could be a million things".{{Ref/Reuse|HNC3}} Before the fragment's destruction, recon drones and survey teams had discovered no less than five unique examples of organisms capable of such extreme states of biological stasis that they challenged the conventional understanding of [[Wikipedia:Abiogenesis|abiogenesis]], the process by which inanimate matter becomes life, or vice-versa.{{Ref/Film|Id=Recon|HNF|Story=Halo: Nightfall Second Stories|StoryLinkText=Second Stories|Episode=RECON-14}} Swarms of Thanolekgolo survived the harsh conditions of the ring fragment and eventually posed a life-threatening obstacle for an [[Locke's team|ONI team]] searching for a unique [[Bioweapon|bioweapon]].{{Ref/Reuse|HNC3}}

==History==
[[File:HaloConstructionCEA.jpg|thumb|250px|left|Sentinels finalizing Installation 04's construction process.]]
===Construction and early history===
The [[Forerunner]]s had Installation 04 constructed by the [[Foundry (location)|Foundry]] of [[Installation 00]]<ref name="p371">'''[[Halo: Primordium]]''', ''page 371''</ref> approximately around the same time as the rest of the [[Halo Array]], circa [[97,445 BCE]] during the [[Forerunner-Flood war]].{{Ref/Site|URL=https://www.halowaypoint.com/en-us/news/canon-fodder-array-with-words|Site=Halo Waypoint|Page=Canon Fodder - Array With Words|D=23|M=12|Y=2019}} The array was designed by the Forerunner [[Builder]]s to combat the parasitic [[Flood]] by eradicating them and all [[Sentience|sentient]] life in the [[Milky Way]]. After the rings were built, Installation 04 and its fellow Halos were distributed from Installation 00 to positions across the galaxy through [[slipstream space]] [[Slipspace portal|portals]].{{Ref/Reuse|halo array}}{{Ref/Film|HLeg|Story=Origins}}

When the [[IsoDidact]] activated the Array at the [[Forerunner-Flood war]]'s conclusion, ending the centuries-long conflict, Installation 04 was the first to fire,{{Ref/Novel|Sil|Chapter=String 38}} followed shortly after by the other six Halo rings. Installation 04 lay dormant for a hundred thousand years, with [[343 Guilty Spark]] and his [[Sentinel]]s ready to keep the [[Flood]] confined in the [[Flood containment facility|Flood containment facilities]] and keeping the infrastructure of the Halo in perfect working order.

===Intermediate period===
After eons of uneventful existence on Installation 04, 343 Guilty Spark eventually found himself bored. For his own amusement, Spark began an experiment in which he evacuated entire sections of the Installation into space; according to Spark, these were experiments to measure the geologic effects of exposure to the vacuum of space and the eventual biological recovery of the evacuated sections, in order to gain insight into emergency response scenarios.{{Ref/Game|CEA|CEA:Terminals#Terminal 4|Terminal 4}}

Around [[40,000 BCE]], an [[unidentified alien vessel]] crash landed in [[Sector 1215]]. Sometime prior to the crash the ship started broadcasting a distress signal.{{Ref/Game|Id=terminal5|CEA|CEA:Terminals#Terminal 5|Terminal 5}}{{Ref/Game|Id=time|CEA|CEA:Terminals#Terminal 6|Terminal 6|Quote=I have now endured 60,000 years without word from outside the Array.}} After attempting to translate it, [[343 Guilty Spark]] blocked the signal, as no communication revealing the location of any of the Halos was allowed.{{Ref/Reuse|terminal5}} After no lifeforms exited for several days, Spark had a large sarcophagus constructed around the vessel.{{Ref/Reuse|time}}

Between the activation of the Array and the arrival of the UNSC and the Covenant, a number of space-faring species stumbled across the installation. Although they reportedly explored the facility and recorded their findings, all of these species eventually left without breaking containment.{{Ref/Game|H2|Conversations from the Universe|Detail=343 Guilty Spark's Log}}

===Discovery and destruction===
{{Main|Battle of Installation 04}}
{{quote|Halo... It's finished."<br>"No, I think we're just getting started.|Cortana and John-117 after the destruction of Installation 04.}}

[[File:Autumn Arrival.png|thumb|250px|The {{UNSCShip|Pillar of Autumn}} arrives at Installation 04.]]

The Covenant discovered the location of Installation 04 after the Covenant [[Fleet of Particular Justice]] followed the {{UNSCShip|Pillar of Autumn}}, which was fleeing from the [[Fall of Reach]] through [[slipspace]]. The Halos are deeply ingrained into the Covenant's [[Covenant religion|religious dogma]], but prior to this discovery they had never actually found one. Due to the Covenant's faster slipspace capabilities, they arrived before the ''Pillar of Autumn''.

The ''Pillar of Autumn'' arrived around September 19, 2552 and was promptly shot down by the warding Covenant ships. Shortly thereafter, the Covenant ground forces on Installation 04 accidentally unleashed the Flood from captivity. [[Human]]s, [[Flood]], and the Covenant fought massive battles against one another as the Forerunner constructs tried to control the outbreak by activating Halo. The ring's monitor, [[343 Guilty Spark]], tried to convince the [[John-117|Master Chief]] to activate Halo. Not knowing the truth of what it did, he attempted to light the ring but was stopped by his AI friend and companion Cortana who was in [[the Core]]. She informed the Master Chief of Halo's true purpose and stashed the [[Activation Index]] in her memory banks. The Monitor betrayed the two and tried to kill the Master Chief and retrieve Cortana, but the two escaped and started plotting against him.

[[File:H2A-AlphaHaloDestruction.jpg|thumb|left|250px|The destruction of Halo.]]
In the conclusion of the battle, John-117 detonated the ''Pillar of Autumn''{{'}}s [[Fusion drive|fusion reactors]] in order to destroy the ring. The explosion critically damaged the superstructure below it; the resulting shockwave and damage to the ring's systems destabilized the ring, shattering it into pieces.{{Ref/Level|CE|CE:The Maw|The Maw}}{{Ref/Note|The particulars of Installation 04's destruction differ throughout its various depictions. In ''Halo: Combat Evolved'', ''Combat Evolved Anniversary'' and most [[terminal]] depictions, a portion of the ring next to the ''Autumn''{{'}}s explosion is sent flying to the other side where it bisects the ring, further splintering the superstructure. The most noticeable change is in the flashback portion of the level ''[[H2:The Heretic|The Heretic]]'' in ''Halo 2: Anniversary'', where the fragment is no longer propelled to the other side and the ring simply shatters, with the explosions spreading in both directions of the epicenter in a chain reaction. The blue lights on the outer surface are also seen going out in this version. The [[H2A:Terminals|''Halo 2: Anniversary'' terminals]] give two versions of the ring's destruction, the first (in Terminal 4) being identical to ''Halo: Combat Evolved Anniversary''{{'}}s [[CEA:Terminals|Terminal 11]], which is closer to the original ''Halo: Combat Evolved'' mechanics, although the ring's shattering is more violent. The second version, shown in Terminal 12, is closer in line with the depiction in ''Halo 2: Anniversary'' version of the flashback in ''The Heretic'' and lacks the shard being blasted to the opposite side.}}

Only a handful of humans and Covenant survived the battle. 343 Guilty Spark floated through space to a [[Threshold gas mine|gas mining platform]] over Threshold, where he stumbled upon a Covenant expeditionary force. Inspired by his words, they began a [[Sesa 'Refumee's heretic faction|heretical]] rebellion against the greater Covenant. Installation 04's destruction is seen as the first step in the chain of events that led to the [[Great Schism]]. The Heretics were quelled by [[Arbiter]] [[Thel 'Vadam]] who silenced their leader, but the seeds of a rebellion were planted. The Monitor was then captured by the loyal Covenant and later defected to the humans' side until he was destroyed on the replacement Alpha Halo by SPARTAN-117 with the help of Sergeant Johnson.

Installation 04 was the first Halo installation encountered by humanity, as well as first to be destroyed. Its attempted firing triggered the activation of a portal leading to [[Sarcophagus|Shield World 006]] within [[Onyx]],{{Ref/Novel|GoO|Chapter=20|Quote=That timing coincides with the activation of an alien weapon world - before John thankfully destroyed it. It is no coincidence that the Sentinels appeared then. It must be part of a larger Forerunner plan.|Quotee=Dr. Catherine Halsey}} and also caused [[Installation 00|the Ark]] to start constructing a [[Installation 08|replacement ring]].

===Debris field===
[[File:H2A - Alpha Halo remains.jpg|thumb|250px|The burning wreckage of Installation 04, surrounded by vessels of the Covenant armada in the aftermath of the battle.]]
Installation 04's destruction left behind a large field of debris, with a few large chunks of the ring remaining.{{Ref/Level|H2|H2:The Heretic|The Heretic}} Some smaller pieces of Installation 04 have landed on Basis, while others have burned up in Threshold's atmosphere upon entry.{{Ref/Map|H2|Burial Mounds}} [[Alpha Shard|One damaged fragment]] notably made a slipspace jump as a safety measure, and ended up in a distant system.{{Ref/Reuse|wp shard}}

====The ''Mona Lisa''====
{{Main|Outbreak onboard Mona Lisa}}
Following the return of the survivors from the battle, the Office of Naval Intelligence learned of the Flood lifeform. Section III sought to establish a research laboratory in order to control the Flood parasite and possibly weaponize it against the Covenant. A science team headed by Major [[John Smith]] was authorized to take command of the [[prison ship|prison vessel]] ''[[Mona Lisa]]''. After bringing a group of Covenant prisoners aboard, they jumped to the wreckage of Alpha Halo in the Soell system. Some Flood specimens had survived the ringworld's destruction and were recovered to be experimented on both human and Covenant prisoners. However, the Flood soon broke quarantine and infected the ship. ONI later dispatched a [[prowler]], the {{UNSCShip|Red Horse}}, to assess the status of the ''Mona Lisa'' under the pretenses of investigating Halo's debris field. On October 25, 2552, the prowler was forced to destroy the overrun vessel with a [[Shiva-class nuclear missile]].{{Ref/Reuse|EvoTML}}

===First replacement===
{{Main|Installation 08}}
Shortly after the destruction of the Halo, [[Installation 00]] began to automatically construct a new Halo to replace Installation 04. This exact copy of the first Halo ring was nearing completion only a few months after the first ring was destroyed, but was also subsequently [[Raid on Installation 08|destroyed]] when it was fired before it was ready by John-117 and Cortana. 343 Guilty Spark attempted to prevent this, but was finally destroyed by the Master Chief with the help of Sergeant Johnson in the new ring's [[Control Room]].{{Ref/Level|H3|H3:Halo|Halo}}

===Post-war===
The UNSC's [[Treaty of 2552|peace treaty]] with the [[Swords of Sanghelios]] forbids either party from landing on the remains of Installation 04.{{Ref/Reuse|nf1}} There is a 500-[[Wikipedia:Light-second|light-second]] exclusion zone surrounding the former site of the ring. In [[2556]], [[Spartan-IV]] [[Fireteam Apollo]] was [[Operation: SHELL GAME|deployed to the exclusion zone]] in direct violation of the treaty; there they recovered some items of value, including a "black box" from the Covenant cruiser ''[[Undiminished Entelechy]]''.{{Ref/Generic|Heading=[[Halo Legendary Crate]]|Subheading=[[Halo Legendary Crate/Data Drops|Data Drop #3]]}}

At some point after the war, a Spartan-IV reconnaissance team was deployed to [[Basis]]. Wearing [[VECTOR-class Mjolnir]] armor, a variant designed for artifact retrieval, their mission was to assess the debris of Alpha Halo scattered on the moon's surface.{{Ref/Game|H5G|[[VECTOR-class Mjolnir]] armor description}}

[[File:HM - Alpha Shard.jpg|thumb|left|200px|Swarms of [[Thanolekgolo]] on the Alpha Shard.]]
====Lost fragment====
{{Main|Alpha Shard}}
When the ''Pillar of Autumn''{{'}}s reactors went critical, Installation 04 attempted to activate a safety measure and make a slipspace jump. However, this self-preservation protocol was only partly successful,