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 enough body mass 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 terra forming abilities, implying their natural environment differs significantly from earth-normal.

Little is currently known about the Flood. It is known that the Forerunners came in contact with them at some point tens of thousands of years before the events depicted in the Halo series. 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 Halo's. The Halo's 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 of 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 millenia 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 'Pillar of Fire' and an unknown covenant ship commanded by a Hierarch and an 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. 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 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 oppurtunity 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 prompts the installation's AI 343 Guilty Spark to recruit the a Spartan II super soldier from the human faction, Master Chief, in retrieving the Index. The index is a device that is the key to activating Halo and preventing the Flood from spreading beyond the facility.

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 destory the ship which was done by opening a hyperspace 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 her or her team-mates they had stowaways. Jenkins insanity warnings, due to his partially flood transformed body, eventually got through to her and she destroyed an important energy transfer cable with a grenade, this dissconnected the connection between the engines and controls. The ship fell back into the gravity of the Installation and everyone aboard was killed.
 * The third attempted 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 rector 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 cable holding the station above the Gas Gaint, plunging 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 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 life’s where 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. Due to the ending with Cortana being held prisoner by Gravemind, it is unclear what his next plan of attack is.

Biology and Life Cycle
The Flood appears in three primary forms: Infection, Combat and Carrier 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.

Flood forms can create a creature to organize the Flood, and on the Infinite Succor, they were seen building such a creature, bringing bodies for it to absorb. What this creature is, is unknown. There is a possibility that it could be a sort of "Brain" form (see below), or perhaps even a Gravemind type of creature.

Infection forms
The infection forms are small, tentacled creatures which have their own defined biological framework, and therefore are not dependent upon a host. Individually they are weak and fragile; one can kill an Infection form simply by squeezing it. However, their tendency to swarm in vast numbers makes up for their delicacy.

An infection form will seek out any sentient life of capable bio-mass 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, which will attack any sentient life it comes in contact with.

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.

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.

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Carrier forms
An infected host can also mutate into a Carrier form. Carriers grow large sacs which contain 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.

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

Brain forms
"Brain" forms are large, spongy Flood forms which resemble a large bag of flesh with tentacles. Presumably, they are used to collect information on important things, such as codes, planet locations and information about the species that the Flood can infect.

Captain Jacob Keyes was assimilated by this Flood form. Over time the Brain form 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 intelligent, and can communicate vocally. It also seems to be able to interact with machinery, as it can use Halo's teleportation grid.

Pure Forms
!Under Construction! Pure Forms are evolved from Infection Forms that have not found a host. Their mutagenic cells form muscle and skin tissue over captured skeletons.

Stalker Form
Stalkers are the basic Pure forms. They are incredibly agile. when they find a good spot, they metamorphosize into the turret-like Ranged Forms.

Ranged Form
Ranged forms are mutated from Stalker Forms. They can shoot long needles at enemies.

Tank Form
the tank form is a huge, grotesque creature that rivals the Hunter in size. It can beat up opponents or spit infection forms at them.

Flood details
"The Flood" were probably named as such due to their overwhelming numbers. However, it may also be a reference to the Great Flood which wiped out the sinful in the Biblical story of Noah's Ark. This is supported by the existence of an enormous, enigmatic Forerunner structure believed to be located under the ruins of Mombassa's outskirts known as "The Ark" which can remotely control the Halos; the only thing that saved Noah from the Flood.

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)