Within a few centuries of its founding, Blackmire's growing population and own internal crime began providing them with enough workers to mine the ore without needing to import criminals from elsewhere. While mining for ore is still brutally hard work, the survival rates rose dramatically as terraforming gradually made the mountains more hospitable. As the mountains became more livable, the inmates were relocated to living quarters closer to the mines. Initially, they expanded the prison quarters as needed. But eventually, Blackmire began to run out of space for their own prisoners.
The original subterranean colony wasn't an option. Most of it had long since been refitted as sewage works. And the parts that remained had been taken over by vagrants, outcasts, some wild fae, and the occasional lesser demon. So Blackmire constructed a floating prison. They bought derelict battle airships and refitted them for a new purpose. They named their prison Hyperion, after the one of the first airships in their fleet.
The fleet of interconnected airships was staffed with a skeleton crew of automatons with the mission to perpetually circumnavigate the globe. While common criminals dig for ore in Blackmire's mines, the most violent and dangerous criminals were sent away to Hyperion Prison. The automatons pilots kept the fleet high above the oceans that cover most of the northern hemisphere. Except for a few secure areas guarded by battle automatons, like the bridge and areas essential to the ships' operations, the prisoners were allowed to roam freely amongst the interconnected airships. The only escape was to fall to one's death in the waters below.
No one knows the first ship in the Hyperion Prison fleet was originally commissioned by Vastienne, an ancient demigoddess of magic who rules over the city from the shadows. She needed it to imprison a wild demigod, a giant boar with immense strength and zero impulse control. The demigod moved into the valley containing Blackmire's farms. The High Council begged her to intervene.
The beastly demigod was extremely territorial, and it thwarted Vastienne's relocation attempts time and again. She couldn't kill it, not that demigods can't die, but demigods killing demigods sets an extremely bad precedent. They learned their lesson from the Gods' War that destroyed their old world. So Vastienne built an inescapable prison for him, one floating high above the earth from which he drew his strength. It was such a good prison, Blackmire began exiling all their dangerous elements there. And then the other city-states began paying Blackmire, handsomely, of course, to take their own mortal refuse and lock it away in Hyperion.
Blackmire sent criminals and supplies to the prison every six months, when its course brought it relatively close to the city, but otherwise the inmates were left to stew on their own. Over the centuries, they developed their own society, of sorts, a strict hierarchy based on strength and power. Nearly a thousand years ago, it was taken over by a powerful sorcerer named Thiriophon who had the power to control beasts.
At first, he started out controlling the rats that had infested the ships, inadvertently introduced during supply drops. And also cats, which were intentionally introduced to help with the vermin problem. Using an army rodents and cats as protection and weapons of terror, he rose through Hyperion's ranks. As his powers grew stronger, he could control the livestock used to feed the prisoners, causing stampedes and anarchy as needed.
But then he discovered a secret prisoner caged in the bowels of the Carnifex, the oldest and strongest airship in the Hyperion Prison's fleet. His bestial magic drew him down there, where he discovered a wild demigod with immense strength, shaped like a giant boar. It took years, but eventually Thiriophon's powers grew strong enough for him to subdue the great beast and forcibly bond with it. With a familiar that strong, his sorcery grew even stronger. Stealing power from the demigod still hidden in the unbreakable cage holding it, Thiriophon tore his way up through the Hyperion ranks with his bestial army, and declared himself king. His strength, and the strength of his descendants, drew followers seeking safety, power, glory, etc. and the "House of Hyperion's" influence continued to grow. Until eventually they were considered divine.
Only the most powerful sorcerers in Thiriophon's bloodline were able to control the demigod's power, though. The weak who tried to bond with it were slowly driven mad. The latest god-king of the House of Hyperion, Thiriophon IV wasn't strong, and his sanity was sapped away over the years by his constant struggle to control the beast. When he looked into the demigod's eyes, the demigod looked back, and it found him wanting.
Thiriophon IV told himself he was the one in control, but he was blind to the truth. He knew, deep down, that he wasn't powerful enough. His obsession with amassing power became all consuming. He was a brutal god-king, slaughtering his own subjects at the slightest suspicion of disloyalty.
His paranoia, although born of growing madness, wasn't entirely unfounded. As the population had grown, some through added inmates, but more so through breeding, the supplies Blackmire sent were not lasting as long as they once did. Though they bred their own livestock and had started growing crops in terrace gardens, there were more and more mouths to feed and dwindling space. But even if there had been enough food to go around, medical supplies were in short supply compared to the population.
The ministers who actually conducted the business of running the fleet, had long since instituted a policy of rationing. The higher ranking members were of course given priority, and hoarding food and other supplies was common. New arrivals found themselves on the bottom of the totem pole alongside the lower ranks and the weak. Between illness and starvation, the "commoners" were on the brink of revolt.
After his own son died of an infection from rat bites, Thiriophon IV blamed Blackmire for the shortage of supplies and medicine. It wasn't hard to stir fervor among his people, and so they began preparing for war. Thiriophon IV's ministers tried to convince him to set his sights on Blackmire's fertile farming valley. But Thiriophon IV wanted to get his hands Blackmire's true source of wealth and power, the ore mines.
With the ministers' direction, the population, which had already turned scavenging, reusing, and upcycling into an art form, began building weapons and tools to overpower the automatons that still controlled the fleet's course. After a successful, but bloody, coup, the inmates of Hyperion Prison finally ruled the entire fleet. They turned south, towards land, and began raiding their way east towards Blackmire's ore mines.
When Blackmire discovered their outposts and territories were being attacked by their own prison, they too began preparing for war. Blackmire had its own military might in the form of the Metropolitan Guard, but Hyperion had the distinct advantage of higher ground. And Blackmire's merchant airships would be no match for Hyperion's armada of reinforced battle airships, which had been resupplied during their raids. So Blackmire hastily assembled a militia, conscripting able-bodied, and usually unwilling, soldiers from civilian ranks.
The militia was originally intended as just cannon fodder, obstacles to throw at the Hyperion fleet to slow their progress towards the mines. The High Council just wanted to buy time as they scrambled to find ways to take down the Hyperion airships they had spent considerable money on refitting in the first place.
While Blackmire's leaders rushed to arm and armor merchant airships, they sent the militia upstream, into the breach on ill-equipped airships the city had commandeered. But the Blackmire militia was filled with the descendants of criminals, not to mention actual criminals hauled from prison cells to fill ranks. The militia had their fair share of crafty operators. They began using guerilla tactics, sending small strikes teams under the cover of darkness to reign terror among their enemies. Despite their lack of proper equipment or back-up, they had a huge impact on the enemy's morale.
It took over two years of painstaking, bloody progress, with heavy losses on both sides, but Hyperion eventually made it to the skies above the mines. By then Blackmire's forces were better equipped and their airships actually stood a chance against the Hyperion battleships. The Guard was still absent from the frontlines, though. They were held back by the High Council to protect the city during air raids from Hyperion ships separated from the fleet and sent ahead to raid and demoralize.
After a total of three years spent fighting, the Hyperion Uprising was finally stopped when a small militia force penetrated the flagship, the Carnifex, and assassinated Thiriophon IV. Then they set his ship ablaze with some kind of magical blue fire that burned cold. It incinerated all living things in its path but leaving non-organic material like metal, glass, and treated wood untouched. As the strange, terrifying flames spread, the remainder of the fleet retreated in panic. The Hyperionites tried to break apart the interconnected ships, but they didn't succeed in time. The flames spread throughout the fleet. Some were spared, safe behind closed bulkheads the fire couldn't penetrate. But their safety was short lived. After drifting for days without pilots, the burnt ships finally crashed into the desert wilds below the mountains.
Thousands upon thousands of Hyperionites died in those few days, either in the flames, the panicked mayhem that followed, or the crash itself. Only a few hundred managed to survive. Those who had been sent to Hyperion as inmates were recaptured and condemned to death for insurrection. Most of the remaining survivors had been born in Hyperion, the descendants of the prisoners, and they were not allowed in Blackmire. They had nowhere else to go, so they stayed in the wilds where they landed, trying to eke out an existence in the cold, barren desert.
It's been forty-three years since the Hyperion Uprising. To this day, no one knows the source of the fire, but those who witnessed it and survived will never forget. Few speak of it, and when they do, it's in hushed tones, as if afraid they will draw its attention.
All that remains of Hyperion is a salvage operation. A handful of roughnecks live in a Blackmire outpost in the low hills at the base of the mountains. Hyperion refugees live in a shanty town called New Hyperion, built among and around the wreckage itself. Any materials of value and/or use are scavenged, bought, sold, stolen, and fought over.