The Flood

The Flood is a parasitic virulent life form, which appears in the Halo Universe. They are depicted as a highly virulent and deadly race, and can quickly incapacitate and infect different life forms, but the infected subject must have sufficient body mass and some level of sentience to sustain the infection forms, such as a Human or Sangheili (Elite) physiological make-up.

Origin and History


Like many things about the Flood, their origin is a complete mystery. It is unknown where they came from or if they have a home planet, but what is known is that they originally lived in an environment that is noxious to most other living creatures, as 343 Guilty Spark and Cortana both comment on the Flood’s terraforming abilities, implying their natural environment differs significantly from Earth-normal.

Little is currently known about the Flood. It is known prehistoric Humanity encountered the parasite first, thousands of years before the events depicted in the Halo series. The first known "arrival" of the Flood occurred some time prior to 110,000 BCE, aboard automated starships of unknown origin that came from the Magellanic Clouds. The crashed remains of these ships were first discovered by ancient humans on worlds near the border of intergalactic space. The vessels, which were found crashed on both inhabited and deserted planets, contained millions of glass cylinders filled with a fine desiccated powder, which was found to consist of inert, short-chain organic molecules of unknown purpose.

Humanity studied the material and deemed it to be harmless, but noted that it had psychotropic effects on lower animals. Small dosages were administered to Pheru, popular domestic animals among humans and San 'Shyuum, which resulted in more docile behavior. Unbeknownst to the humans or San'Shyuum at the time, the powder was altering the genetic code of the Pheru, manifesting as improved behavior while slowly changing other aspects of their genome.

After several centuries, more disturbing changes appeared. Pheru treated with the powder began exhibiting furry growths and fleshy protrusions, which other Pheru were compelled to consume. Shortly afterward, the Pheru began suffering widespread abortions and genetic deformities, and many were euthanized or released into the wild. Soon afterward, the humans and San'Shyuum who had been in the presence of the altered Pheru began to exhibit some of the symptoms of the powder-induced "disease."

Affected on a psychological level by the strange illness, infected victims began to consume the sick Pheru, and parts that were discarded also became vectors for the disease. The afflicted then moved on to cannibalism and sacrifice of the uninfected. The infected humans and San'Shyuum proceeded to spread the disease into other systems, which furthered the scope of the Flood outbreak.

At this point, the Flood infestation, which had previously been predominantly a mind and behavior-altering affliction with only relatively minor physical changes, began to reshape its victims into a variety of forms designed to gather victims, engage in combat, and to rapidly consume useful biomass and other resources. The growing outbreak quickly led to a conflict between humanity and the Flood.

During the Human-Flood war, Humanity managed to create a cure for the Flood. This landed such a devastating blow to the parasite that they were not heard from again until the Forerunners' first contact at at G617 g1. Unfortunately, the cure was lost when Humanity was devolved by the forerunners as punishment for the Human-Forerunner war.

Many confrontations and disasters followed, eventually resulting in the Forerunners instituting a variety of construction projects in order to curb the threat. This varied from war fleets to numerous research installations and weapons platforms constructed all over the galaxy. Varying from shield world installations such as the miniature Dyson sphere known as Onyx, to the massive orbital installations known as Halos. The Halos in particular served the dual purpose of quarantined research facilities and more importantly, as the delivery system of a super weapon energy pulse capable of wiping out all sentient life of sufficient bio-mass to sustain the Flood in the entire galaxy.

In the event of a Flood escape despite the containment procedures, and assuming all other strategic possibilities were exhausted, the Halo System was designed to be fired, cutting off vectors by which the flood might spread. 343 Guilty Spark states that the Halo System was fired once before when it became clear that there was no hope of ending the Flood/Forerunner war by conventional means. The plan worked, and although unthinkable amounts of sentient life were wiped out, the Flood was halted from spreading and starved to death for lack of sustenance... eventually allowing the galaxy to re-populate in an un-infested environment. Despite this measure, some Flood specimens survived in the research facilities aboard the Halo installations themselves, entering into a state of suspended animation and surviving for millennia in dormancy.

During the events of the Halo trilogy, the Flood were re-awakened when both Humans and Covenant began to uncover and interfere with the now ancient and abandoned Forerunner Installations. Unknown to the rest of their respective species, the Flood were first encountered by the Human ship 'Spirit of Fire' and an unknown covenant ship commanded by The Prophet of Regret and the Arbiter when both ships stumbled upon and fought over an unknown miniature Dyson Sphere disguised as a planet.

Several confrontations took place involving all three factions, and the reason the Flood was active and uncontained at this particular facility are unknown; though it is likely that it was a battlefield during the Flood/Forerunner War, the Flood being the obvious victors. It is known the humans were unable to pass along information about this threat back to the main UNSC government or forces due to extensive damage to their ship. Whether the Covenant were able to escape and communicate the threat is not explicitly stated, but it is heavily implied as they seem to conduct themselves with a degree of foreknowledge aboard Alpha Halo 20 years later.

During the events of the first Halo, the Flood were accidentally unleashed by the Covenant, decimating all other factions on the Installation and spreading at a frightening rate. The Covenant retreated, suppressed and sealed the entrances but a team of UNSC marines lead by Captain Keyes of The Pillar of Autumn, unwittingly unsealed the Flood, sealing the fate of Installation 04. With the Covenant and UNSC forces battling one another, the Flood saw an opportunity to spread further than the boundaries of the Installation and set their sights on spaceships currently in Orbit. There were three recorded attempts to board and repair ships and leave Installation 04.

The release of the Flood on Installation 04 prompted the Monitor of the Installation, 343 Guilty spark, to seek a reclaimer to retrieve the Index. Conveniently, there was one on board the installation: Spartan-117, John, Master Chief Petty Officer.

After the Master Chief retrieves and begins to use the Index, the true nature of the Halo rings is revealed by the Chief's own AI, Cortana. Discovering that Halo's defense system is a weapon designed to kill all sentient life in the galaxy, which the Flood need to spread. When confronted with this information, 343 Guilty Spark states that the installation technically only has a maximum radius of twenty-five thousand light-years, but that its pulse would trigger other similar installations as well, killing all sentient life in the galaxy.


 * The first was when a force of Flood managed to take over the Covenant supply/agriculture ship Infinite Succor. A strike team led by Rtas 'Vadumee (Half-Jaw) was sent to investigate a distress signal from the ship. After a series of loses on the Rtas 'Vadumee side, the only way to win the battle was to destroy the ship which was done by opening a slip-space window to the nearest sun, the Prophet on board tried to change Rtas 'Vadumee's mind to no avail. It is presumed the ship, with the Flood on it was destroyed entering the sun, but it is not confirmed.


 * The second attempt was when the flood tried to board and leave on the Truth and Reconciliation. This attempt was less successful, as Covenant forces were able to defend their ship, but due to their dwindling numbers they were instead over run by Marines commanded by Major Silva. Major Silva was about to leave Installation 04 on the Truth and Reconciliation but unknown to him or his team-mates they had stowaways. Jenkins insanity warnings, due to his partially flood transformed body, eventually got through to First Lieutenant Melissa, an ODST under Silva's command, and she destroyed an important energy transfer cable with a grenade, this disconnected the connection between the engines and controls. The ship fell back into the gravity of the Installation and everyone aboard was killed.


 * The third attempt was to use a badly-damaged Pillar of Autumn. It was heavily damaged due to wounds inflicted in a fire fight with Covenant ships and the later crash landing: this meant the ship was over looked by the Covenant. When the Flood infected a number of Marines and workmen who served on the ship, they were able to acquire the knowledge about the ship systems and began repairs. They were interrupted by Covenant forces, the Master Chief and 343 Guilty Spark with Sentinels. The Master Chief later set the fusion reactor core on the Pillar of Autumn to overload which caused the resulting explosion to destroy Installation 04.

Heretics had commandeered a Forerunner station in the gas giant Threshold that Installation 04 orbited. The station was already holding The Flood for defensive study by the Forerunners. The Flood overran the station, and the Arbiter cut three cables holding the station above the Gas Gaint, plunging it into the heart of the planet.

The second outbreak happened on Installation 05, also known as Delta Halo to the humans. This outbreak by the Flood was far more advanced and organised, with the Flood managing to take over the Covenant High Charity, using a number of UNSC Pelican drop ships from a crashed In Amber Clad to board the giant floating city. On Delta Halo, Gravemind revealed himself to Master Chief, the Arbiter and Cortana, his reasons for saving their lives were not found until Master Chief saw Pelican drop ships carrying The Flood. Master Chief and the Arbiter were only a diversion for Gravemind's plan. Eventually, Gravemind rooted himself in High Charity most likely using the teleportation grid, and the Flood took control of High Charity. During these events, one of the human AIs, Cortana, was captured by the Flood and interrogated by the Gravemind, who was hoping to corrupt the AI into leaking important information. To stop this from happening, Spartan 117 was dispatched to retrieve or destroy Cortana. During the crusade Master Chief was transmitted messages from Medicant Bias, a corrupt Forerunner AI. When he finally confronted the Gravemind, it was revealed that the Gravemind was going to rebuild his invasion force on Installation 04 and Installation 00, the Ark, by crashing High Charity into Installation 00.

Biology and Life Cycle
The Flood appears in four primary forms: Infection, Combat, Carrier and Pure forms, but also have more mysterious forms such as the "Brain" form. The flood will consume all sentient life it comes in contact with, and can mutate its hosts into various forms to help it do so.

There are three stages in the evolution of a flood colony:
 * 1) Feral: This is the first stage of the evolution: the flood species will work as individuals and will attack anything they see – even each other.
 * 2) Colonial: This is the second stage of the evolution: the flood species first start showing signs of ethological behavior. They form a hive mind and start building a "brain form".
 * 3) Civilizational: This is the final stage of the evolution: this stage is triggered when the colony reach a critical biomass; when they first start making a gravemind. This is the most dangerous of the stages: it is the point when all flood forms are united and actually start thinking like a hivemind, and reach human-level intelligence: they can coordinate attacks on specific locations; attacks on specific targets and start utilizing technology.

Infection forms
The infection forms are a type of "pure" flood spawn. They have a very strange anatomy: they are small, tentacled creatures which have their own defined biological framework, and therefore are not dependent upon a host. Individually they are weak, parasitic creatures which will try frantically to take over a host; together, they can easily overwhelm a platoon of fully armed marines.

An infection form will seek out any sentient life of capable biomass and calcium deposits to sustain itself, and proceed to attempt to use the creature as a host. The infection form parasites attack in a flood-like swarm (hence the Flood moniker) that rapidly advances on host organisms, then physically attach themselves to a host as they try to burrow into its chest. Once inside the organism will begin to modify the host's genetic code through mutagenic spores and take over. The infection form does this by tapping into the spinal system, suppressing the host's consciousness, embedding itself in the thoracic cavity, and releasing spores which cause the host to mutate. At this point, the infected creature can mutate into a variety of other flood forms.

Combat forms
If the Flood finds a suitable body, it will infect the body and become a Combat form. These Combat forms are the front-line troops of the Flood: the species the Combat forms originate from can vary. A combat form can only be developed when there are sufficient levels of calcium in the host: if not, the host will not generate a combat form but instead will generate a carrier form.

When the flood infects an animal, living or dead, it absorbs the knowledge of its host. This knowledge can be communicated to other flood using unknown methods. This was demonstrated aboard the Infinite Succor, a Flood-infested Covenant ship. When the Covenant sent a strike team to the Infinite Succor, the Flood managed to capture a few Elite units. After absorbing the knowledge of the Elite, the Flood on the ship became more organized, setting up patrols and creating defensive positions.

Combat forms are extremely strong and agile. They also gain the ability to jump very long and very high distances. The Combat units are able to use weapons that their hosts were able to use, and gain any kind of advantage their host had biologically. The Elite-derived combat forms are sometimes able to use the energy shielding technology with their remaining Elite armor.

Combat Flood are also capable of unarmed combat, striking with whip-like tentacles protruding from the arms of the host. These tentacles can grow out of the arm at an alarming rate, simply breaking the nearby bones and displacing them.

The combat forms see through the small feelers and tentacles sprouting out of where the head used to be. These are the tentacles of the Flood Infector that resides within the host.

Flood combat forms totally ignore any threat to themselves and those fighting alongside them and will often kill themselves to kill an opponent. Most of the time, Combat forms fight until their bodies are no longer capable of doing so, at which point they are either discarded or possibly turned into Carrier forms. Blowing of the head of a combat form will do absolutely nothing, as the head is not utilized by the Infector and simply pushed aside.

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Carrier forms
An infected host can also mutate into a Carrier form. Carriers grow large sacs which incubate several infection forms. When a carrier is in close proximity to any number of suitable hosts, it triggers some manner of biochemical reaction, causing the sacs to explode and spread the infection forms in order to infect more hosts.

Carriers are slow and walk with a comical waddle, flailing their tentacles as they stumble towards the enemy. The explosion is quite forceful and is capable of doing damage to anything caught within the blast. This is their only offensive mechanism and portrays them as suicide bombers.

It is unknown what the criteria are for a host to become a carrier form. All answers are speculative at best.

Proto-Gravemind
Proto-gravemind are large, spongy Flood forms which resemble a large bag of flesh. Tentacles sprout from the body and anchor to the surrounding environment. They are used to collect information on important things, such as codes, planet locations and information about the species that the Flood can infect, and if they have the right body such as Captain Keys can pilot a ship.

Captain Jacob Keyes was assimilated by this Flood form. Over time the Proto-Gravemind strips memories and information from its victims, but is not able to take memories that the victim is trying to hide from it (in Keyes's case, the location of Earth). All body tissues and bones are soon reduced to fluid, and are digested as the brain slowly absorbs the information. It is unknown how this information is communicated to other Flood forms, or if it is at all. (Halo: The Flood)

Gravemind
The Gravemind, and its place in the Flood, is enigmatic. The Gravemind is sentient and possesses a sort of hive mind control over the rest of the flood. It can communicate vocally. It also seems to be able to interact with machinery, as it can use Halo's teleportation grid. The Gravemind has a flair for the dramatic, and even recites poetry. The Flood is shown to be a hivemind with the Gravemind at its core (physically separate beings, but the gravemind controls their conscience). In Halo 3, the gravemind influences other flood sub-units to assist the Master Chief in stopping the Prophet of Truth from activating the Halo rings.

Halo 3 "Morpher forms.
!Under Construction! Morphers are highly advanced Flood forms only seen very recently since their discovery. According to research, they are formed when sufficient biomass has been accumulated by the Flood. Calcium from the bones of the Flood's victims makes up the structure of the Morpher. Through some means as of yet unknown, the Morphers have the ability to alter their structure, and possibly the make-up of their structure, as a response to different combat stimulus.

Upon death Morphers do not fall apart into a pile of limbs and "flood crust"

Stalker Form
Stalkers are the basic Pure forms. They are incredibly agile, and vaguely resemble an elongated, flattened, and enlarged Infection Form. Their head is the most common trait of all Pure forms, with a pair of thick tentacles framing a mouth full of Flood sensor antennae, while their abdomen, which is possibly made up of a torso of a human or similar creature, stores calcium for transformations. They have four limbs, the rear pair of which end in splayed feet used for walking, while the front pair end in scissor-like claws used in combat. However, the Stalker is very ineffectual in combat, and prefers to transform into one of the other Pure forms to fight. The Stalker moves in a spider-like fashion, climbing walls and ceilings, and is capable of extraordinary leaps. They often drop from ceilings to ambush whatever is walking underneath.

Ranged Form
Ranged forms are tripodal Pure forms. These forms are turret-like in appearance and are quite tall. They are often found hanging from walls or ceilings, from which they fire sharp spikes at enemies. The nature of these spikes is assumed to be that of battlefield detritus and shrapnel, but could also possibly be that of excess calcium converted into fragmented shards. In any event, these shards are the main identifying feature of this form, standing in multiple, somewhat organized rows up the front side of the creature's body. Physically weak, they are highly susceptible to damage from the front. To counter this, they curl into a ball to protect their weaker spots when attacked, and are able to transform into the Tank Form enemies approach too near.

Tank Form
The Tank form is a bipedal Flood Pure form, with large, asymmetrical arms formed from the majority of the Pure form's calcium structure. Physically the strongest and toughest Pure form, the Tank Forms are very imposing, standing head and shoulders above average humans. They use their massive strength and hardened fore arms to tear through their enemies, and are capable of surviving what would kill pretty much anything else. They can generate Infection forms, regurgitating them out of their mouths during lulls in combat. Tank forms are possibly used as a means of mobile communication for the local Gravemind, although there is only one documented instance of this. Tank forms are all but invincible when it comes to ballistic/energy ranged weaponry save for shots delivered to the face centre where its fan-like tentacles lie, however the Tank form may attempt to shield its face with its arms when fired upon.

Flood details
The termonology "flood" is derived from the Latin: Tecktius Flood. This is translated exactly as: "The apocalypse in physical". This is the first of the theories of where the name "flood" is actually derived from. It could also just be a nickname given to it by marines due to its tendency to swarm, like "the waters of the rising flood". One final theory is that it is a reference to Noah and the flood that ruined the Earth. This appears likely as there are many symbols relating to Jewish and Christian religion in the Halo universe (seraphs, prophets, the Ark, Halo etc.). This would mean the Flood are believed to pose the greatest threat to the safety of the universe.

The Flood can terraform the atmosphere to suit them, as was seen on High Charity. Fleshy growths were attached to the walls, and the air became damp and gaseous. The Gravemind also took residence, and was able to use a Covenant speaker system to broadcast messages. (Halo 2)

Flood weaknesses
Flood of any kind are highly susceptible to ballistic weaponry, explosives and fire. A reason the Covenent was weak to flood attacks was their use of energy weapons.