The Goliath Mortars had ceased their rhythmic pounding, but the silence on the surface was more ominous than the bombardment. Through the silver-mirrored periscope, Kael watched the Imperial lines. They weren't reloading shells; they were moving heavy, insulated copper tanks toward the fresh craters. The "Golden Finger" warning at the base of his skull didn't fade with the end of the kinetic strikes; it sharpened into a localized, searing heat. Vane was preparing a "Promethean Bore"—a focused chemical fire designed to liquefy the limestone roof and pour white-hot slag into the residential tiers.
Kael knew that no amount of iron or peat could stop a sustained thermal breach. Limestone, when heated to extreme temperatures, would calcine and crumble, losing all structural integrity. To survive the fire, the mountain had to become the opposite: a cryogenic fortress. He initiated the Ice Shield project—a desperate plan to use the Bio-Foundry's refrigeration equipment to flash-freeze the moisture within the upper limestone strata, creating a thermal barrier that would defy ignition.
The technical core of the project was the Ammonia-Expansion Cycle. Kael utilized the Bio-Foundry's large-scale cooling units, originally designed for medicinal distillation, and reversed their primary flow. By compressing ammonia gas into a liquid and then allowing it to rapidly expand within a network of copper pipes, he could create temperatures far below the freezing point of water.
"We aren't just cooling the air, Elms," Kael said, his breath already beginning to fog in the command vault. "We are going to pump this 'Cold-Loop' directly into the limestone faults. We've already saturated the upper stone with water from the mortar-leaks. Now, we're going to turn that water into 'Glacial Stone'."
The grit of the construction was a logistical nightmare. The Tier 0 crews and the newest Aspirants had to haul miles of thin-walled copper tubing into the jagged, unstable fissures created by the bombardment in Tiers 1 through 3. They worked in the dark, their fingers numb and cracking as they soldered the joints in a race against the Imperial heat-crews. The air in the upper tiers was no longer humid; it was bone-dry and biting, the "Deep-Migration" families shivering as the mountain's "Ice-Blood" began to flow.
Socially, the Ice Shield was a test of endurance. Nearly a thousand people were now huddled in the lowest basalt tiers, the density creating a psychological "Pressure-Cooker." The "Sanitary Corps" had to distribute heavy wool-and-flax cloaks, repurposed from the "Scrap Reclaimer," to prevent a wave of hypothermia. The "Green Ring" grain was struggling; the sudden drop in temperature was causing the "Living Water" in the troughs to sluggishly crystallize, threatening the mountain's food supply.
A technical failure occurred in the Tier 2 "Fault-Line" segment. The copper tubing, brittle from the extreme cold, snapped during a minor seismic settling of the mountain. A high-pressure jet of liquid ammonia erupted into a residential corridor, the toxic gas threatening to suffocate a cluster of "Aspirant" families.
Kael utilized the "Atmospheric Flush" bypass. He didn't send men into the gas cloud. Instead, he opened the primary geothermal steam-valves into the affected corridor. The hot steam instantly neutralized the ammonia gas, turning it into a harmless, if foul-smelling, liquid that was then drained into the "Digester" sumps. It was a waste of precious heat, but it saved the lives of the forty families in the sector.
The first Imperial thermal-drill ignited at dawn.
It wasn't a thump; it was a high-pitched, sustained hiss. Through the periscope, Kael saw a brilliant, magnesium-white flame erupt from the central crater. The heat was so intense it turned the zinc-oxide dust into a shimmering glass. The "Promethean Bore" was eating into the limestone at a rate of inches per minute.
But as the heat traveled downward, it hit the Ice Shield.
In the command vault, the Seismic Mirror showed a new, bizarre pattern—a "Thermal-Clash." The white-hot slag hit the frozen limestone and instantly solidified into a brittle, obsidian-like crust. The extreme temperature differential created a "Thermal-Shock" that shattered the Imperial drill-head, the metal unable to handle the jump from two thousand degrees to sub-zero. The mountain didn't melt; it "flash-quenched" the fire.
The grit of the battle was silent. For hours, the Empire poured chemical fire into the craters, and for hours, Kael's ammonia-pumps hummed in the deep-vaults, maintaining the ice. The mountain became a battlefield of thermodynamics.
The population count remained at 990, but the toll was visible in their faces. They were living in a frozen tomb, their breath frosting the very iron skeletons that held them. Kael stood by the ammonia-pumps, his own hands wrapped in thick leather, watching the pressure gauges. The mountain was holding, but the "Golden Finger" in his head was still humming a low, persistent warning.
"They're going to see the 'Steam-Plumes', Elms," Kael whispered, his voice cracking from the dry air. "The clash of fire and ice is creating a massive white cloud on the surface. It's a 'Beacon' that can be seen for fifty miles. Vane isn't just trying to get in anymore. He's signaling the 'Imperial Dreadnoughts'—the aerial fleet. He's going to stop fighting the stone and start fighting the air."
Kael looked at the "Green Ring." The grain was turning a sickly yellow. They were winning the thermal war, but they were losing the biological one.
"We need to move to Tier 15," Kael commanded. "We need to build a 'Atmospheric-Rebreather'. If the aerial fleet comes, they'll use 'Gas-Bombs' to turn our vents against us. We need to be able to breathe without the surface for a year."
The engineering of the "Atmospheric-Rebreather" was the next step in their evolution—a system that would decouple the mountain's air from the sky entirely, turning Ashfall into a true, self-contained planet within the stone.