Assassin's Creed Valhalla brought back elements of the Assassin's Creed lore from both the historical fiction and the modern day plotline. One of those returning plot elements was the Great Catastrophe.
The Great Catastrophe has been called by several names of the course of the Assassin's Creed games, from the Toba Disaster to Ragnarok. Tying in real world events and mythologies, the Great Catastrophe is one of the most important moments in the Assassin's Creed lore, and is vital to understanding the franchise's fictional history and where the series might be going.
The First Civilization in Assassin's Creed
Assassin's Creed is known for weaving historical fiction with sci-fi, and the Great Catastrophe is no different. The event took place around 75,000 years ago, at the same time that a supervolcano in Indonesia erupted, that has been theorized to have caused a sharp decline in Earth's population. In the Assassin's Creed universe this thesis is a misunderstanding, and the sharp population decline was actually caused by a concurrent coronal mass ejection from the sun, also known as a lethal solar flare.
At the time, Earth was ruled by the First Civilization, also known as the Isu. The Isu were a progenitor species to humanity. Extremely scientifically advanced, the Isu genetically engineered humans to be laborers and Neanderthals as soldiers. However, eventually humanity, led by two humans named Adam and Eve, rebelled against the Isu. While the Isu were very advanced, humanity had numbers on its side. Distracted by the war, the Isu did not notice the coming solar flare until it was too late. Some Isu scientists and leaders did try to prevent the Great Catastrophe, but each one of their plans failed.
Assassin's Creed: The Six Isu Plans
The six plans to prevent the great Catastrophe were were devised by three Isu; Father of Understanding Jupiter, Sacred Voice Minerva, and Mother of Wisdom Juno. Together, they were known as the Capitoline Triad. The first plan involved building four towers, which would draw on the energy of the solar flare, dispel it, and prevent it from wreaking havoc on Earth. One of the towers was partially built before it was discovered that the project would take too long to be ready before the flare.
The second plan was to create a giant magnetic forcefield around Earth. This would have repelled the solar flare using the same technology as the Rings of Eden, hand-worn Pieces of Eden which could repel projectiles. However, the plan proved too large to pull off, even to protect just a small portion of the population.
It wasn't until an Apple of Eden was used to experiment on humans that a third potential plan arose. It was discovered that when a large number of humans believed in an idea while targeted by a Apple of Eden, that idea would become reality. The third plan involved shooting an Apple of Eden into space, turning it back towards the Earth, and then getting all of humanity to think the phrase "make us safe." As bizarre a plan as it is, the problem that undid it turned out to be oddly mundane. The Isu couldn't figure out a way to turn the Apples of Eden around once they'd fired them into the stratosphere.
Realizing that any plan to save the First Civilization as it had once existed was doomed to failure, the Capitoline Triad began experimenting with less conventional ideas. The fourth plan was to physically augment the Isu so that they would be able to live in the sun-scorched post-apocalyptic world. The plan involved reinforcing the Isu's bodies with steel, but the process quickly proved to be a non-starter. Juno's husband Aita was the volunteer, and ended up asking his wife to euthanize him when his mind and body began deteriorating.
The fifth solution was to try and find a way to move the consciousnesses of the Isu into a computer that would be able to withstand the solar flare. They struggled to develop the technology, though as the Assassin's Creed games so far have shown, it is in fact possible to move a consciousness into a computer. The sixth solution came when Minerva realized that there were equations underlying existence itself. Though complicated, she believed that it was possible to use these to travel backwards through time to stop the Great Catastrophe, but the method itself was too dangerous.
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Future Catastrophes
Minerva then created the Eye, a machine which would allow the user to manipulate reality's underlying code using her new knowledge, and protect Earth. However, it turned out Juno had altered the machine so that, if used, she would gain total power. Instead, Minerva's knowledge was used to send messages from the Capitoline Triad to Desmond Miles and his ancestors. Over the course of the first three Assassin's Creed games, this led Desmond to find the Isu's Grand Temple and eventually prevent a similar solar flare from wiping out life on Earth in 2012.
In order for Desmond to prevent the Second Disaster, however, he had to let Juno out of the Grey, a network where her consciousness was imprisoned. Juno's story ended up being resolved in an Assassin's Creed comic, but the consequences of Desmond Miles' decision to activate the Isu defense mechanisms in the Grand Temple still have effects by Assassin's Creed Valhalla's modern day storyline.
The magnetic field used to prevent the Second Disaster also had the effect of causing the Earth's magnetic field to slowly increase, disrupting the environment and human technology. In a twist on the third game's ending, however, Valhalla's modern-day player character Layla ends up becoming trapped in the Grey when stabilizing the Earth's magnetic field. With her is a being called the Reader, implied to be Desmond Miles, who says they can work to prevent the next Great Disaster. The Great Disaster and its consequences may have been averted yet again, but only the next game will tell if another extinction-level event can be prevented.
Assassin's Creed Valhalla is available now for PC, PS4, PS5, Stadia, Xbox One, and Xbox Series X.