Halo Array

"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

The Halo Array, known individually as Halos or Halo rings, referred to by the Covenant as the Sacred Rings, and labeled Fortress Worlds and Installations by the Forerunners and Monitors, is a system of colossal ring-shaped superweapons.

The first array of twelve Halos was constructed by order of Master Builder Faber circa 101,000 BCE with the intent of being an ultimate weapon, one that would secure the pre-eminence of the Builder rate in Forerunner society. Later, the weapons would be refined further and a new array of six smaller and significantly more lethal rings was constructed. 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. All 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.

Background


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. Built following the Human-Forerunner War, these ringworlds were used thousands of years later 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 containment facilities, including the Halo installations themselves.

A total of eighteen Halo rings existed during the reign of the Forerunners; an older array of twelve 30,000km rings produced by the greater Ark and six 10,000km rings constructed at the newer lesser Ark. Of these, only seven survived to be included in the final Array. The two most well-known Halo installations, Installation 04 and Installation 05, both orbit gas giants, though this is not the case with all Halos; Installation 03 orbits a rocky planet. Installation 04 maintained an atmospheric mining facility in Threshold's atmosphere until it was destroyed by the Covenant.

Though separated by thousands of light-years, the installations are networked together and capable of remote activation at the Ark, an extragalactic megastructure. Each Halo installation has a maximum effective range of 25,000 light-years in every direction. The method utilized by the array to conduct this "mass sterilization protocol" 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.

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, with the exception of the Ur-Didact, who had been imprisoned within Requiem. Some Forerunners survived at the lesser Ark but evidently chose to exile themselves from the galaxy. The array has come close to activation three times since; Installation 04 was almost activated by the Master Chief, Installation 05 was activated by Commander Miranda Keyes at the behest of the Brute Chieftain Tartarus, and Sergeant Johnson was forced by the Prophet of Truth to activate the Array from the Ark. None of these attempts were successful; the first was stopped by Cortana, while the second and third were halted by UNSC and Covenant separatist intervention. A replacement Halo for the destroyed Installation 04 was successfully activated outside of the galaxy, eliminating the Flood massed at Installation 00, but it was incomplete and thus not networked to the rest of the Array.

Each of the Halo installations in the final Array is given a designation number, from 01 to 07, and is overseen by a single monitor. The monitors are given control of the Installations' Sentinel automatons, from Aggressors to Constructors and Enforcers, and are responsible for containing the Flood test subjects in their research facilities and protecting the Halo from intruders.

The Array also encompasses Installation 00, an extragalactic construction facility that can create replacement Installations in the event that one is destroyed. All Installations can also be remotely activated from the Ark, as the megastructure is out of the Array's range. The Forerunners also built shield worlds as a means to escape the effect without having to leave the galaxy.

Construction
The Halos were constructed by the Master Builder and his Forerunner Builders several thousand years after early humanity first encountered and drove the Flood from the Milky Way. 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. Although they faced strong opposition from the Prometheans, including the Didact, for thousands of years, the faction eventually won the approval of the Council and commenced work on the Array.

However, at this point, the Librarian went to the Council and invoked the Mantle, stating the 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. 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.

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 lesser Ark. The final array, activated at the conclusion of the Forerunners' conflict with the Flood, was comprised of seven rings, each 10,000 kilometers in diameter.

Forerunner-Flood war
The first test of a Halo installation was conducted by 05-032 Mendicant Bias, who fired Installation 07 in 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 a Precursor from captivity on the former planet. Mendicant Bias then brought the released Precursor to the Halo for study and began a 43-year-long interrogation of it.

Following the use of Installation 07 by Master Builder Faber to suppress 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 since the San 'Shyuum rebellion, and assaulted the capital. He 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 slipspace jumps, yet only one escaped before the portal collapsed, with the other six breaking up in-slipspace.

Installation 07 then jumped into a distant system on a pre-designated destructive collision course with 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.

Later, as Mendicant Bias prepared his final assault on the Maginot Sphere, the IsoDidact finally accepted that the Halo Array was the only solution to counter the Flood, and activated the Array. Installation 04 was first in the Array to fire, with the others following sequentially as their fields intersected. The effect left all Flood-controlled ships adrift, allowing Offensive Bias to defeat and capture the rampant AI.

Post-activation
The seven Halos then remained relatively dormant for approximately one hundred thousand years, though at least one of them experienced a major Flood outbreak, and at least one have experienced brief visits by other species, including a major crash-landing in 40,000 BCE.

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 humanity 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 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 "Great Journey" and join the Forerunners in godhood.

Rediscovery


Eventually, the stellar coordinates of Installation 04 was discovered through the combination of a crystal artifact on Sigma Octanus IV and a huge Forerunner artifact buried under the surface of Reach. The coordinates were utilized by the '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 Marines led by Captain Jacob Keyes accidentally broke quarantine again, expecting to find a large Covenant weapons cache. The human-waged guerilla war quickly turned into a massive four-way battle between UNSC forces, the Covenant, Sentinels led by 343 Guilty Spark, and the Flood.

The battle finally culminated when Spartan John-117 detonated the fusion engines 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.

Later, the Covenant discovered a second 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, another four-way conflict began. The battle ended in the Flood manifesting a Gravemind and successfully escaping the ring aboard infected Covenant ships. The ring was nearly activated by Tartarus, the 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 Forerunner Dreadnought in the center of the structure, activating it. However, the structure was soon revealed not to be the Ark, but a generator of a portal to the actual Ark, a massive artificial world located outside the galaxy. Human and Covenant separatist 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 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, along with the Ark.

By January 2553, the UNSC had begun an active search for the remaining Halo Installations. By March 2553, the Office of Naval Intelligence had successfully located at least one, Installation 03, and constructed a research station, Ivanoff, in its orbit. By at least July 2557, UNSC scientists were studying the Array for decommissioning, with facilities at Installations 03 and 05. At the asteroid field orbiting Installation 03, the scientists located the Composer and accidentally activated it, causing them to become digitized. However, the sensor data left over from the incident led to the discovery of the shield world Requiem. Later, the Didact traveled to Ivanoff Station near Installation 03 to retrieve the Composer and used the device to kill the entire research staff before heading for Earth.

Custodial
The Installations are designed to be run by advanced artificial intelligence constructs specially purposed by the Forerunners. The highest intelligence on each Installation is a single Monitor. The Monitor's task is to ensure that the installation's Sentinels, which range from Constructors to Aggressors and Enforcers, 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. Monitors also have access to their respective installation's defensive system.

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 Majors 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.

Save for the Monitor, all automatons can be constructed at specialized production facilities that float high in the Halo's atmosphere. They seem to contain almost limitless materials for constructing an almost indefinite number of automatons.

Environment
After Master Builder Faber's plans were co-opted by the Librarian, the Halos were given terrestrial surfaces to support catalogued 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. The Halo installations support a wide range of environments, habitats, ecosystems, and climates. Installation 04 and Installation 05 supported warm, temperate forests that were both deciduous and coniferous, swamps, and cold, snow covered tundra environments. Installation 00 had climate ranging all the way from tundra, to forest, to desert. It is unknown whether this range is shared by all the Halos, but the similarity of these environments and that of Installation 00 makes it likely.

While the terrain of a Halo ring may appear to be naturally formed at first glance, it is actually artificially constructed. Strato-Sentinels extract raw materials from the source, process them in transit, and deposit building materials at the Installation. 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 super-structure, and tugged in place by centripetal force. The installation's buildings are then built by Constructors and Sentinels. 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. Some features, such as landslides, are the result of time, and have been formed naturally. Others, such as the myriad network of tunnels and cave systems that riddle the installation's internal structure, are transit conduits used by the ring's Sentinels and Enforcers. 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.

Technology
Each Halo has several assets that are uniform to all installations. Each contains a Control Room located somewhere upon its inner surface, from which a Reclaimer must manually insert the installation's Activation Index to activate it. Each also possesses a Library, a large structure protected by an energy shield, where the Index is housed and protected by Sentinels. The index itself is a semi-solid 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, including its inner passages and networks, to be used as a navigational reference for traversing the installation. Flood containment and 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.

Installations also contain advanced teleportation grids, allowing instantaneous transportation for a Monitor or Reclaimer to any place on the installation. These grids cannot be controlled by the Flood, though the Gravemind was able to use that of Installation 05 by controlling 2401 Penitent Tangent. For Sentinels, the installation is riddled with tunnel and cave networks for access and transportation. The Sentinel portals are connected to factories via tunnels.

The Halo rings achieve their "gravity" through centripetal force. As the ring spins, centripetal force pushes all spinning bodies away from the center of rotation. The ring is uniform, and because of this, all points are the same distance from the center, therefore centripetal force applies evenly. This force also pushes objects on the surface of the ring away from the center of rotation, or pushes them down on the surface of the ring, translating into gravity. When the 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.

The Halo installations are also equipped with drive engines spaced along their rim. In the event of an emergency, a Halo can maneuver itself to avoid damage from a collision or weaponry. In addition, they possess hard light reinforcement to stabilize and protect them against tidal and gravitational forces from other objects. One of the most extraordinary systems possessed by the Halos is their ability to lock entire sections of the ring, or, if necessary, the entirety of it, into reflective slipspace stasis. This effectively suspends these sections in time and renders them invulnerable to damage from the outside and allows the occupants of the ring to survive the main weapon's firing. However, it also consumes an enormous amount of energy.

The Halos are capable of repairing themselves to some degree, replacing damaged plates of foundation material and restoring biological sections. Rings with a 30,000 km diameter could also be reduced to a smaller size by shedding large portions of the foundation. In order to prevent the ring from falling apart during this process, it can generate a hard light hub with spokes which hold each of the foundation plates in place.

The rings of the second Halo Array are 10,000 km in diameter; this size is roughly similar to that of Earth, which is 12,756 km in diameter. The surface of each ring is 318 kilometers wide. The original twelve Halo rings were 30,000 km in diameter. Each installation in the final array orbits a large, dense planet which serves as a gravitational anchor. 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.

Firing method
The original twelve Halos were designed to fire laterally, cleansing specific planets or systems within a relatively small area of effect; the six smaller Halos (and the reduced Installation 07) were designed to fire spherically, (in all directions), killing all sentient life within three radii of the Milky Way's center. When activated, the Halo rings release a burst of cross-phased supermassive neutrinos. This burst of neutrinos is carefully tuned to possess a harmonic frequency, which destroys 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 the system of Charum Hakkor.

This pulse is propelled across the Halo Array's full radius at superluminal speeds and will eventually propagate at a near-infinite velocity; this was known to generate paradoxes with causality when the rings first fired, with two of the Halos reporting pre-echoes of the combined activation before the rings had been fired. The energy discharge covers the Array's effective radius and cleanses it of all affected life, though simpler life forms that do not possess a neural system, such as microbes, fungi, algae, mosses, and traditional plants are unaffected.

Due to the Forerunners' use of corpse-disintegrating 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.

Function
The Halo Array is complex, but each ring can be activated individually by a Reclaimer, also activating the other installations, 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 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 control panel in order to begin the activation sequence.

The main weapon is amplified by phase pulse generators, three of which are close to the control room, at least on Installation 04. Each installation has a maximum effective radius of 25,000 light-years and functions via form of lethal radiation. The pulse is designed to kill all sentient life in the installation's three-dimensional radius, with the array covering the entire galaxy. The pulse targets the nervous system of sentient life forms via the issuing of a harmonic frequency. The nervous systems of the targeted beings are destroyed, rendering them useless to the Flood; however, the Halo effect does not disintegrate biomass, leaving the victims' bodies mostly intact. 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, Lifeworkers sprayed target biospheres with a solute that would cause any animal killed by the Array to instantly decay into its component molecules, resulting in flash-desiccation.

The only known ways to avoid the effects of these pulses are to seek shelter in a shield world or to escape to Installation 00, which is out of range of the array. Once activated from Installation 00, the other installations will fire simultaneously, eradicating all sentient life in the galaxy, thus starving and killing the Flood.

Trivia

 * The Halos are remarkably similar to the eponymous megastructure of Larry Niven's 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 Orbitals from Iain M. Banks' Culture series, though considerably smaller.
 * The names of the Halo installations are Beta, Epsilon, Kappa, Alpha, Delta, Gamma and Zeta Halo, ordered from 01 to 07 respectively.
 * The Halo textures for both Halo: Combat Evolved and Halo 2 are the same, and are both symmetrical.
 * In a Halo: Combat Evolved prototype, Installation 04 had a section that was only partially constructed. This feature was dropped from the final game, though it may have inspired the design of the second Installation 04.
 * On the screen where Captain Keyes taps his pipe on the opening scene of the Pillar of Autumn, TRAJECTORY FD: HALO is displayed by the hologram of Installation 04, although the UNSC was not aware of the name at the time.
 * In 2011, the Halo Array was the number 1 most "Ridiculously Oversized Videogame Weapon" by PasteMagazine.com.

List of appearances

 * Halo: The Fall of Reach
 * Halo: Combat Evolved
 * Halo: Combat Evolved Anniversary
 * Halo: The Flood
 * Halo: First Strike
 * Halo 2
 * Halo Graphic Novel
 * The Last Voyage of the Infinite Succor
 * Halo: Ghosts of Onyx
 * Halo: Uprising
 * Halo 3
 * Halo: Contact Harvest
 * Halo: The Cole Protocol


 * Halo: Evolutions - Essential Tales of the Halo Universe
 * The Mona Lisa
 * Halo Legends
 * Origins
 * Homecoming
 * Odd One Out
 * Halo: Reach
 * Halo: Cryptum
 * Halo: Glasslands
 * Halo: Primordium
 * Halo 4: Forward Unto Dawn
 * Halo: The Thursday War
 * Halo 4
 * Halo: Silentium