Picture this…
You enlisted in the United Nations Space Command. You wanted to do your part and help to protect humanity against enemies both foreign and domestic. You went through boot camp with hundreds of other aspiring young marines like yourself and formed some good friendships along the way.
Near the end of your stint in training, it came over the comms, humanity was not alone in the universe. Harvest, one of the outermost colonies Earth had established in the Milky Way, was under attack. Not from insurgents or splinter factions, from an unknown alien enemy calling themselves “The Covenant”. What followed was something you hadn’t in your wildest dreams ever thought would come to pass.
A war spanning nearly 27 years in length against an enemy that was vastly technologically superior and resolute in their beliefs. There was a glimmer of hope, The SPARTAN-IIs. They helped to stem the tide, but there were too few of them to make a real impact. Finally the Covenant found Reach, the Human military stronghold housing nearly the entirety of the UNSC armed forces. They attacked without mercy and with overwhelming force. The ship you were assigned to, The Pillar of Autumn, fled the battle carrying, what was believed to be, the last SPARTAN-II and made a blind jump through hyperspace. When the ship emerged out of hyperspace the Covenant were not far behind, but there was an object positioned in geosynchronous orbit around a gas giant, the Halo ring. Having escaped certain death at Reach and not wanting to die in the cold vacuum of space, your Captain decides to abandon the ship and land on the ring.
It’s a rich lush world full of plants, running, water and unknown ancient alien tech.
One day, a comms tech overhears the Covenant talking about a weapon they discovered buried in the ring; something that could wipe them out. Not wanting this weapon to fall into the Covenant’s hands, your captain hand picks a squad to storm the bunker, retrieve the weapon and bring it back. As they storm the bunker they find a mass of dead Covenant and a single locked door. The squad brute forces their way through the door and unknowingly unleashes The Flood on the galaxy.
The Flood sweep across the Halo ring killing everything in their path, Human and Covenant alike. You watch as your friends are lost underneath a swarm of infection forms and slowly begin mutating into flood themselves. This isn’t what you signed up for… even with the Master Chief, there is no escaping this.
…
Your magazine runs dry and you draw your sidearm. There’s only a few of you left, your backs against the wall waiting for Echo 419 to brave the airspace to evac your squad. There is no end to the Flood. For every single one you kill, a hundred more take their place. You watch as your squad are overrun, you fire your pistol until it runs dry as well, you load your last mag and begin counting the shots squeezing off rounds until there’s only one left in the chamber. Your squad’s bodies begin to move and thrash around as they mutate and begin reanimating as part of the Flood’s endless wave. You turn the sidearm and place the end of the barrel against your temple, this isn’t what you signed up for… you never signed up for this nightmare…
Anyone who has played any of the main trilogy of Halo games knows full well who the Flood are and what they can do. But not everyone knows their origin and how they nearly conquered the galaxy long ago during the time of the Forerunners.
HISTORY
Despite what the Halo games have led us to believe, the Forerunners were not the most technologically advanced species in the Milky Way galaxy, The Precursors actually held that title for millions of years. The Precursors actually created the Forerunners and assisted them in their advancement to space faring species. When the Forerunners attempted to take the ‘Mantle’ from the Precursors, the Forerunners were deemed unworthy. This caused a great war between the Precursors and Ancient Forerunners that resulted in the Precursors being expelled from the Milky Way galaxy all together.
‘The Mantle’, or as it is referred to in the games, “The Mantle of Responsibility”, refers to the belief that the most technologically advanced species was charged with the protection of all other life in the galaxy. With the Precursors having been expelled by the Forerunners from the galaxy, the Forerunners assumed the mantle and set to work, work which lasted thousands of years.
Outside of the Milky Way, some of the remaining Precursors entered stasis while others decided that dying was a better end. Those that died eventually dissolved into a dust that was stored in cylinders. Ancient space faring Humanity found these cylinders and opened them. The dust entered the humans’ bodies and began to mutate them from the inside out, eventually giving birth to the first Flood forms and proto-Gravemind. Initially the Flood attacked Humanity but the collective memories of the Precursors deemed Humanity worthy of the mantle and thus, the Flood ceased their attacks, instead moving to attack the Forerunners in the Milky Way. Humanity still fleeing the Flood’s advance, entered the Milky Way ahead of them and began attacking the Forerunners in hopes of breaking through and putting more distance between themselves and the Flood.
Unbeknownst to the Human fleet, a large portion of them had been infected with the Precursor dust.
Around roughly 98,379 BCE, The Flood arrived in the Milky Way. Utilizing captured non military vessels, the Flood managed to bypass the Forerunner defense fleets and land on Forerunner worlds. As the infection took hold on the Forerunner planets, the collective intelligence of all biomass the infection assimilated was provided to the Proto-Gravemind.
After over 300 years of war, the Forerunners began to realize that their extinction was a real possibility. While the Forerunners would win every engagement against the Flood, they were unable to halt the spread of the infection. Eventually resorting to detonating the stars of entire systems to stop large infestations.
The Forerunners began saving and cataloging species to make sure the Flood would not destroy them. One such example was ancient humans. The Forerunners took specimens from ancient space faring humans and after some light modifications, seeded the planet we know as Earth with a new wave of humanity. Some specimens were kept and stored alongside various alien species, such as Elites and even some flood samples in their vaults on the Shield Worlds. After the initial contact, the Forerunner-Flood War entered into a stalemate for several hundred years.
During the stalemate, the Forerunners constructed many different AI to assist in the construction of solutions and deployment of their navy to combat the infection. One of the AIs that was created by the Forerunners was known as 05-032 Mendicant Bias. Mendicant was tasked with interrogation of the captured Proto-Gravemind to determine if the Flood could be reasoned with. The Proto-Gravemind identified itself as the last Precursor when it was interrogated by Mendicant, stating that the Flood was the last salvo in the Precursor-Forerunner war and that they would end the Forerunner race. As the interrogations continued, the Proto-Gravemind began to question Mendicant’s masters until it ultimately swayed Mendicant into believing that the time of the Forerunners was over. This came to be known as ‘The Logic Plague’ which affected not just AI but some of the Forerunner race as well. Mendicant allied with the Flood against the Forerunners sparking the beginning of the end of the war.
As the Forerunners scrambled to fight not just the Flood but now their rampant AI as well, a meeting was called to discuss how to proceed. The Diadect advocated for militaristic action against the Flood. To do this, he would need to compose some of the newly settled humans and turn them into his Knights (of Halo 4 & 5 fame); meanwhile, the master builder proposed the construction of more Shield Worlds and the Halo array. The assembly approved of the master builder’s plan and the Diadect was turned down; though, he would attempt to go behind the assembly’s back and make more knights, he was ultimately stopped and imprisoned in the Cryptum you find him in at the beginning of Halo 4.
As the Flood continued through the galaxy, the Forerunners ran out of options and the Librarian was unable to determine a cure for the infection. Ultimately, the Forerunners activated the Halo Array. The array functioned as it was meant to, killing all living beings with a sufficient biomass for infection. This in turn stopped the Flood and killed off all but the samples the Forerunners had kept in vaults on each Halo ring and on the Ark.
The activation of the array destroyed all Precursor and Forerunner tech that was not protected by either a shield world or a Halo ring. The Flood was starved out with the Proto-Gravemind dying as well. Eventually automated Key ships began ferrying the samples the Forerunners had stored in their vaults to new planets so life could once again foster in the Milky Way without the problem of the Flood.
This is where we start the Halo series. Thousands of years have passed and the Flood have laid dormant in their vaults on Halo.
BIOLOGY
The Flood is a parasitic species of extragalagtic origin which is very virulent in its natural state, its Latin name is Inferi Redivivus which translates to “The Dead Reincarnated”. It can only be classified as an anomaly as it does not follow any known structure of function or organization. It represents the unstoppable force of nature and cannot be contained by conventional means. As the infection takes hold, the parasite forces the host biomass through several stages of “evolution” until it achieves a massive biological breakdown in the host. Once this breakdown occurs then the infection can really take hold and work its magic. While the Flood infection is able to reproduce A-sexually without the use of a host, this is normally seen as a last ditch effort and is only really possible for “Pure Flood Forms”. The Flood has survived for as long as it has by the use of Lysogenic Replication. This is a process wherein the viral cells infiltrate and corrupt the healthy cells infecting them with their own genetic code. This allows the viral cells to mutate the healthy cells into new viral cells to infect other healthy cells. This process occurs until all healthy cells have been turned.
The infection absorbs all biomass indiscriminately with only a very few species proving to be immune from the infection, Hunters and Drones have been shown to be immune to the infection for various reasons. One of the Forerunner’s plans, before the activation of the Halo array, was to utilize the Lekgolo worms that make up hunter colonies to consume the Flood biomass. While it proved effective in isolated cases, it was unable to be deployed on a large scale and the Forerunners were forced abandoned this plan.
The Flood are able to infect any organism with a biomass that is sufficient to house their infection, though, they do tend to prefer organisms with large brain capacity. This helps to accelerate the formation of the Gravemind to control the infection. Since the Flood’s Gravemind intelligence is only as smart as the organisms consumed by the infection, the more intelligent a species is, the more dangerous the infection can be. Having developed in severe conditions, the Flood infection is very resistant. It can survive on all known habitable worlds, temperatures ranging from –75 – +53 degrees Celsius, and can even survive underwater for a short time.
As the Flood assume control of an area, they begin to alter their environment to promote further growth and incubation. They will begin attaching themselves to walls to create pods for breeding the infected virus as well an expelling spores into the air. If left alone for a long enough time and with enough raw biomass to work with, the Flood is able to completely turn a location into a Hive which can house a Gravemind or an entire army of forms (as seen with High Charity following Halo 2). The Flood infection tends to thrive in humid & lush environments which is why during the campaign of Halo 2, the “Quarantine Zone” used to contain the Flood infection is desolate, cold and snow covered.
NEUROLOGY/PHYSIOLOGY
The small bulbous squid looking “infection forms” are the Flood’s basic infectious hosts. They move across the ground looking for dead or wounded biomass with a sufficient sentience that they can add to the collective. Possessing several long tendrils they attack and overwhelm the host before using the tendrils to enter the host and find it’s spinal cord. The infection form then syncs it’s own nerve signal to that of the host and kills the host. From there it assumes control of the host and infects its brain wiping all personal memories. Some information such as combat techniques and technical intelligence is kept by the Flood and added to the Gravemind intelligence. This process is so complete that despite a few small lingering memories, the host is now completely subservient to the Gravemind. It’s only purpose to infect new hosts and protect the Gravemind.
There is another tactic used by the Flood to obtain specific information from a new host. This is the tactic that was used on Captain Jacob Keyes during the campaign of Halo: Combat Evolved. Rather than brute forcing their way into a hosts mind, they ‘burrow’ and slowly take over their memories and thoughts until they obtain the specific information that’s sought. In Captain Keye’s case, the Flood were looking for a starship to take them away from the Halo ring (Installation 04) or to show them the location of the ‘new and rich feeding ground’ (Earth). While Keyes fought them for as long as he could, eventually he was taken by the infection and the Flood gained the information they were after.
A Gravemind is able to override the primal/basic instincts of the Flood and coordinate them into an effective force once enough biomass and intelligence has been obtained through infection. A Gravemind is also able to control the actions of each individual infected host and even use their vocal chords to communicate with other species.
While the neurological infection and assimilation is the same regardless of species, the physiological mutations are species specific. “Higher evolution hosts” such as humans, elites, and forerunners are used as a means of combat and thus their mutations generally result in “combat forms”. These forms retain the basic profile of the host species while still being significantly mutated. Most common mutations are: corrupted organ systems, decayed body cavities, internal organs displaced and decaying outer skin. The nature of these mutations render high powered ammunition, such as sniper rifles, largely ineffective and allows a combat form to remain functional even after being decapitated or maimed. Combat forms also generate large tentacles from their extremities and central core. These tentacles are used as melee weapons and can sometimes contain bony protrusions for added damage.
COUNTERMEASURES
As it stands in the Halo universe, there are no known countermeasures to the Flood infection. Once an infection takes hold of a host there is no way to stop the infection from spreading and there is no known method to reverse the effects of an infection. Flamethrowers are effective in destroying the infection before it attaches to a host, but the most effective form of controlling the Flood is isolating the infection and starving it out.
Certain neurological disorders that affect the neural frequencies of the hosts have proven to render individuals immune to Flood infection. One such disorder is Boren’s Syndrome. This condition which is caused by radiological exposure creates electrical anomalies in the nervous system which the Flood cannot mimic. Sergeant Avery Johnson is the only known individual with Boren’s Syndrome to have come into contact with a flood infection. While he was attacked and was attempted to be assimilated into the Flood, he survived. He does have some Flood DNA in his system but it is unable to mutate him; however, it did gift him with some advanced healing capabilities.
There you have it, the unstoppable infection that is the Flood. It’s rather reassuring that this is a fictional virus and not something we’re dealing with right now. I have spent hundreds if not thousands of hours playing various Halo games and can say that I am terrified of the Flood. It’s something that I hope we would never have to deal with… ever.
Until next time!
The Multiverse 
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