With the collapse of the False-Face, the Imperial blockade dissolved into a series of uncoordinated retreats. The surface was quiet, but Kael did not move the population back to the sun. The isolation had proven a fundamental industrial truth: the deep-vaults provided a controlled environment, free from the seasonal volatility of the frontier. To scale the population to the thousands, he needed more than just a mine; he needed a permanent manufacturing hub. He began the excavation of the Subterranean Foundry, a Tier 5 facility designed to house the barony's first continuous-flow iron works.
The technical challenge was the management of the Forge Atmosphere. A traditional surface forge relied on natural drafts and tall chimneys to carry away carbon monoxide and particulates. In a sealed mountain, a single blast furnace could asphyxiate the entire population in minutes. Kael engineered a Forced-Induction Oxygen Loop. He utilized the high-pressure geothermal steam to drive massive centrifugal fans, which pulled air through a series of "Lye-Scrubbers"—vats of alkaline solution that chemically stripped the carbon dioxide from the forge exhaust.
The grit of the construction fell to the newest Aspirants, the former Imperial smiths who had once served Vane. They worked alongside the original Ashfall crew, carving out a cathedral-sized hall in the lower hematite vein. Instead of portable anvils, Kael designed the Gravity-Drop Hammer—a three-ton iron weight suspended from the ceiling on a rack-and-pinion system. By using steam-pressure to lift the weight and gravity to drop it, the foundry could shape heavy structural beams with a fraction of the manual labor previously required.
Socially, the Foundry Tier changed the nature of daily life. The rhythmic, subterranean thud of the hammer became the heartbeat of the mountain, a constant vibration that reminded everyone of their productivity. Kael implemented a "Hot-Seat" shift rotation. Because the foundry generated a surplus of radiant heat, the workers operated in four-hour bursts, followed by eight hours of recovery in the "Cooling Tiers" near the aqueduct intake. This prevented heat exhaustion and kept the production line moving twenty-four hours a day.
A material failure occurred during the first firing of the Tier 5 blast furnace. The refractory bricks, which had served well for smaller kilns, began to vitrify and crack under the sustained, concentrated heat of the geothermal-assisted blast. Molten slag began to seep into the floor-channels, threatening to breach the primary steam-lines.
Kael utilized the Basalt Injection technique. He ordered the workers to pump a slurry of crushed basalt and water into the cooling jackets around the furnace. The basalt, having a much higher melting point than the clay bricks, fused into a glass-like protective shell on the interior of the furnace walls. It was a self-healing lining that turned the furnace into a geological vessel.
The foundry's first output was not weaponry, but infrastructure. Kael directed the smiths to produce standardized iron "I-beams" and interlocking floor-plates. For the population to grow, the mountain needed to be partitioned into vertical neighborhoods. Every beam pulled from the cooling vats was a skeleton for a new residential tier.
The population count reached 710 as the remaining Imperial stragglers, abandoned by Vane, were processed through the steam triage. These men were not just laborers; they brought with them the "Tactical Memory" of the capital. One such man, a senior quartermaster, pointed to the growing stack of I-beams and noted that the Empire used similar shapes for their heavy border forts, but they lacked the precision of Ashfall's steam-pressed joints.
Kael stood on the observation gantry, looking down at the sparks flying from the drop-hammer. The transition was working. They were no longer a group of survivors in a hole; they were an industrial entity. The iron was moving, the air was clean, and the mountain was expanding downward and outward.
We've reached seven hundred, Elms, Kael said, his voice carrying over the roar of the fans. But the foundry needs more than iron. It needs a massive, consistent supply of "Flux"—limestone is fine, but for the high-tensile alloys, we need manganese. The seismic mirrors show a rich deposit two miles east, beneath the Imperial ruins. We need to extend the rail-line without Vane's scouts seeing us.
Kael began mapping the "Deep-Rail" expansion—a subterranean transport system that would connect the mountain to the surrounding resources, turning the entire valley into a hidden network of industrial veins.