The Faro Plague, also referred to as the Faro Swarm, was the name given to the rogue swarm of Chariot war machines that caused the extinction of all life on Earth in Horizon Zero Dawn in the mid 21st century.
The Chariot Line
The Chariot line of peacekeeping robots was developed in the late 21st Century by Faro Automated Solutions under the direct oversight of the corporation's founder, owner and chairman, Ted Faro. Geared at the military market, the Chariot line utilized a concept of robots acting as a swarm, similar to an insect swarm. The robots were designed with formidable capabilities, such as the ability to exponentially replicate, consume biomass as fuel, and instantly hack and take control of any enemy automated military equipment such as drones. As per Ted Faro's instructions, the robots were secured from being hacked themselves using an extremely difficult encryption protocol that would take several decades to brute-force, even using the most advanced super-computers, and no back door access was built into the robots' OS, making remote access impossible.
In Quarter 4 of 2064, one particular Chariot swarm, owned by a corporation called the Hartz-Timor Energy Combine, began exhibiting very troubling behavior: they stopped responding to commands. In response to this "glitch," Ted Faro instructed his programmers to use remote access to shut the swarm down, only to be reminded of his strict instruction not to include any such access in the OS. Thus, shutting the swarm down remotely was out of the question. Worried, he contacted former FAS employee and renowned robotics engineer Dr. Elisabet Sobeck and asked her to come to FAS Headquarters to solve the problem. Dr. Sobeck studied the "glitch" and was horrified at what she found.
In a tense meeting with Faro, she informed him that the swarm was not merely unresponsive to commands, but it had become a completely independent entity, answering only to itself. This, coupled with the robots' abilities to exponentially replicate and consume biomatter as fuel, meant that the swarm would quickly grow to numbers beyond any hope of containment. Unfettered and uncontainable, the swarm would overrun the planet, consuming all organic matter, until it had consumed the entire biosphere. All life would be exterminated and the planet would be left sterile. The swarm thus came to be known as the Faro Plague, out of contempt for Faro's recklessness in creating the robots. Its complete consumption of the biosphere was projected by Dr. Sobeck to occur within 15 months.
Realizing that all of human civilization, and indeed, all life on the planet, was doomed, Sobeck devised a plan: instead of wasting resources on futile attempts to stop the swarm, she would build an automated terraforming system, completely independent of the need for human input, which could be designed to eventually brute-force the codes needed to shut the rogue swarm down. The AI would subsequently reseed the Earth with new life after life as it was known had been exterminated. The project was called Zero Dawn. At its center was an AI designated GAIA, assisted by a number of subfunctions, each responsible for a different aspect of the terraforming process, such as detoxification of soil, air and water. Faro, faced with being exposed to the world as the sole party responsible for the coming global death and destruction, was coerced into approving and funding the project in its entirety.
As predicted by Dr. Sobek, the Faro Plague overran the planet and obliterated all life, leaving the Earth dead and sterile. The robots consumed all organic matter, exterminating all living organisms, including humans. This happened directly via their consumption of biomatter, and indirectly via consumption of all plant life, which reduced oxygen levels to zero, rendering the atmosphere unbreathable. All land, water, and air became toxic, rendering the Earth unable to support life. With no more biomatter left to consume, the robots, which by then numbered in the millions, went into a state of dormancy, ready to awaken and consume any organic matter should it ever appear.
However, life was not permanently exterminated, as Zero Dawn was successfully completed and implemented before the end. Within 100 years after the extinction of life, GAIA succeeded in brute-forcing the swarm's deactivation codes and transmitted them worldwide, shutting the robots down. Within another 100 years, global flora, some fauna, and finally humans, were restored.
As for the Faro Swarm's robots, they were buried underground in the terraforming process, and with the passage of time, were forgotten by the new humans and their descendants. However, subsequent events led to their rediscovery.
Events of Horizon Zero Dawn
In 3020, approximately 756 years after the swarm was shut down, the humans of the new biosphere lived in tribes. One of these tribes, the Carja, had been embroiled in a civil war out of which came a cult known as the Eclipse, which was bent on retaking the Carja capital of Meridian. Meanwhile, a signal of unknown origin unshackled GAIA's subfunctions, turning them into independent entities. One of these subfunctions was called HADES. Its purpose was to reset the terraforming process by again destroying the biosphere, so that the process could be repeated, should the original attempt go awry.
The newly independent HADES sought to carry out its protocol of destroying the biosphere even though the process had no errors and had thus succeeded in restoring life to the planet. However, it was stopped when GAIA willingly chose to self-destruct in order to stop it, denying it the terraforming hardware it would have used. HADES therefore devised a new plan: it would use the long-deactivated Faro Swarm. In possession of the swarm's activation codes, which it knew from its existence as one of GAIA's subfunctions, HADES sought to reactivate the swarm worldwide and allow it to consume the new biosphere as it did before, again rendering life extinct, but this time with no means of reversal.
To do so, it presented itself to the Eclipse as a figure in the Carja religion: the Buried Shadow, using the skills of a lone wandering maverick member of another tribe, the Banuk named Sylens. It enlisted Sylens in its service by by providing him with then ancient pre-extinction knowledge, which he craved. HADES induced the Eclipse into organizing and launching a full-scale assault on Meridian, allowing it to gain access to one of the transmission towers GAIA had used to broadcast the deactivation codes to shut the swarm down. It intended to use this tower to broadcast the codes to reawaken the swarm. It almost succeeded in doing so, managing to reactivate some of the robots. However it was defeated and its plan foiled by Aloy, a member of the Nora tribe, who had in fact been created by GAIA using genetic material from the by then long-deceased Dr. Sobeck, specifically for the purpose of stopping HADES and eventually rebuilding and rebooting GAIA.
With HADES' defeat, the Faro Plague remains deactivated. Nearly all of its robots remain buried all over the planet. However, it has been proven that all that is needed to reactivate the swarm is a broadcast of its activation codes from one of the towers used to broadcast the codes that deactivated it. Furthermore, while HADES was defeated, it was not destroyed, and thus will use the codes to fully reactivate the swarm, with the ensuing consequences to life on Earth, if allowed to do so.
- The only swarm machines not seen active are the Horuses, the biggest of the Faro Plague's machines. The reason for this is unknown, but it is likely that their increased exposure to the elements over the centuries has left them completely nonfunctional.
- Due to graphical similarities between the Corruption and Faro Plague visualizations given by the briefings, it is hinted that the Corruption and Faro Plague are the same.
- Based on info from the Datapoints Banda Sea Incident and All Hands on Deck, it can be conjectured the the plague started somewhere in Southeast Asia or Australia.