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IO, a new underground city built by humans and synthients

IO is a new underground human city, built by free humans and their Synthient allies after the fall of Zion. It is led by General Niobe.[1]


For many years after the Battle of Zion, there was peace between the free humans and Machines. As more and more Redpills were allowed to leave the Matrix, however, the Machines began to experience an energy shortage. In time this led to the Machine Civil War, in which the Machines divided into several factions competing over scarce resources, and eventually the Analyst usurped the Architect to seize power over the Matrix itself.

Morpheus had been elected High Chair of Zion's Council, but he believed in Neo's sacrifice and that the Machines would never break the Truce he died to secure. He was only half-right: the Architect was indeed true to his word, but the new power rising in the Machine world that overthrew him cared more about its own survival. Zion was devastated in an attack - though it was not an utter massacre, and the survivors managed to evacuate. This was due to a combination of the Analyst's faction being only a fraction of the total Machine armies, Zion being stronger after years of peace, and many free Machines even siding with the humans.

Led by General Niobe, Zion's remnants founded a new underground city at a hidden location, and named it "IO". As the decades passed the Machine factions in the ongoing civil war were more concerned with fighting each other, so they ignored the hidden city, giving it the opportunity to not only rebuild but actually flourish to a greater extent than Zion ever did. Unlike Zion, with its "us versus them" siege mentality, IO was built by humans and Machines working together, which would have been impossible before Neo's sacrifice.

Realizing that they could never fight off the Machines in a prolonged siege lasting for years, Niobe instead decided on the strategy of hiding the city as best as possible, using a complex holographic projection. Strict access protocols were also implemented, though some came to feel that as IO flourished, they became more concerned with their own safety than trying to free all of humanity still trapped in the Matrix.

The hovership Mnemosyne enters IO.

Niobe continued to lead the city until she was 90 years old, at which time her chief of security and right-hand man is Sheperd. In the years after the city was founded a few hoverships still freed a trickle of humans from the Matrix, and in one such mission Niobe personally freed Bugs - a young woman who insisted that she caught a brief glimpse of Neo still alive but trapped in the Matrix. Few believed her, but in time Bugs rose to be captain of her own hovership, the Mnemosyne, and assembled a small but like-minded crew of true believers who never gave up hope in Neo's legacy, who continued to search for him.


Neo gazes out from a balcony at IO's main cavern.

IO is built in a large underground cavern, but in an improvement over the old Zion, it actually has its own artificial sky of sorts (made from light panels) and even its own atmosphere and weather - water vapor released from the planet's sediment, to create a layer of clouds near the ceiling of the cavern.

IO has not only recovered but advanced to a better point than Zion was able to achieve, as the free humans only had about a hundred years in each Matrix cycle to try to resettle the real world. With sixty more years, and the combined efforts of humans and Machines (who prefer to be called "Synthients"), IO is even starting to make limited progress in restoring the biosphere, recreating real agricultural crops. Nearly all real world species have gone extinct, but their genetic profiles were sequenced and stored in the Matrix. An ecological restoration project led by Niobe's advisor Freya and the Synthient Quillion has managed to re-synthesize DNA based on these files and re-create several species. Among the first plant life they have successfully recreated are strawberry crops, along with butterflies to pollinate them, and they're on the verge of bringing back blueberries.

Much of the ground level of IO's cavern is therefore covered in farmland, while all the facilities and living chambers are built into the cavern's massive pillars, rising like skyscrapers.


  • The name "IO" seems to have a double-meaning. Reading it as letters, it seems to be an acronym for "Input/Output". Read as Roman numerals it is "10" - and "10" is "2" in binary numbers, in line with the naming of machine city 01. This could mean that IO represents the second chance for machines and humans to coexist together peacefully. "IO" is also the middle letters of "Zion", but with the first and last letters cut off - perhaps a reference to having no beginning and no end and/or forming from a remnant of Zion.
  • Additionally, Io was a princess in Greek myth who was loved by Zeus. Zeus changed her into a heifer in order to hide her from Hera, much like the city of Io is hidden from its enemies by an illusion.
  • Io is also a Japanese unisex given name which can be written in a number of ways with several meanings: the first Kanji in the name is usually 依 (i) meaning "rely on" combined with any of the following: 皇 (o) meaning "emperor", 桜 (o) meaning "cherry blossom", 緒 (o) meaning "thread", 生 (o) meaning "live", 雄 (o) meaning "hero, manly", 旺 (o) meaning "prosper" or 央 (o) meaning "centre, middle". Several of these meanings have potential symbolic relationships to the city of Io in the film.