The Arcs had started as social and technological experiments. Man made structures that were utterly self-sufficient. They grew their own food, processed their own waste, had their own water and generated their own power.
In their original form they were heralded as the future of cities. No longer did the great urban landscape need to destroy the natural one. As the experiment was tried, and refined the Arcs moved from just self-sustaining cities to completely closed off eco-systems.
In theory, it was claimed, they would survive a complete ecological collapse. The residents of the Arc could live there for generations and their grandchildren could leave, once the world had recovered.
When the global political situation started to deteriorate a handful of influential figures, led by Holly Branson, created the Arc Project. The project was funded by a conglomerate of independent leaders who wanted to ensure continuity of human knowledge and endeavour.
Five Arcs were originally planned. One each in Switzerland, Argentina, Canada, South Korea and Australia. Each of the Arcs was a to be a self-sustaining population of 50,000 to 100,000 people. Anyone on the planet could apply to join any of the Arcs, though in reality the more education, money or profile you had the more likely you were to get a coveted spot.
In the end only two Arcs ever made it to completion, and even they could not completely escape the Pandemic. Once the Winter set in the managing boards of the two Arcs made the decision to seal the doors, and let the experiment run its course.
Over the last few decades a small handful of people have left the Arcs. Usually it isn't their choice. But sometimes they run. When that happens others are sent to find them.