The population of Ashfall had reached 790, and the biological strain on the mountain's closed-loop system was becoming visible. The air in the lower tiers was growing heavy with the scent of recycled oxygen, and the protein-heavy diet from the fish vats was no longer sufficient to sustain a labor force working the deep-rail and the foundry. To reach a population in the thousands, Kael needed more than oxygen scrubbers; he needed a primary producer. He initiated the construction of the Green Ring—a Tier 7 circular gallery designed to wrap around the primary geothermal bore, utilizing its radiant heat and a new system of artificial lighting to create the mountain's first industrial-scale farm.
The technical core of the Green Ring was the Photonic Core. Kael could not rely on the dim, pale glow of bioluminescent algae for high-yield agriculture. He utilized the geothermal steam to drive high-speed turbines connected to a series of refined "Arc-Lamps." By passing an electrical current from the galvanic cells through a gap between two carbon rods, he created a brilliant, intense light that mimicked the spectrum of the sun.
The grit of the construction involved the "Terracing of the Void." The Tier 7 gallery was carved into the limestone in a series of concentric, descending steps. Kael engineered a Vertical Hydroponic System, where nutrient-rich water from the aquaculture vats was pumped to the highest terrace and allowed to trickle down through a series of gravel-filled troughs. The plants—mostly fast-growing tubers, leafy greens, and a hardy variety of dwarf grain—were not grown in soil, but in this constant flow of "Living Water."
Socially, the Green Ring transformed the psychology of the deep-vaults. For the first time since the blockade began, the citizens could see something green and growing. The "Green-Keepers"—a new labor tier made up of former surface farmers and Aspirants with a knack for botany—managed the light cycles and nutrient ratios. The ring became more than a farm; it became the mountain's lungs, a place where the air was always crisp and smelled of damp earth and growing things.
A biological failure occurred during the first month of the "Grain-Cycle." The high humidity of the Green Ring, combined with the lack of natural wind, led to a sudden outbreak of "Stone-Mold"—a white, fuzzy fungus that began to consume the stalks of the young grain. If it spread, it would rot the entire crop and contaminate the mountain's air with spores.
Kael utilized the Atmospheric Agitator. He realized that the plants needed "Mechanical Stress" to strengthen their stalks and prevent the air from stagnating. He repurposed the small "Sonic-Damping" fans from the deep-rail to create a constant, artificial breeze that circulated through the terraces. He then introduced a mild sulfur-steam "Fumigation" from the geothermal bore, which killed the mold without harming the plants.
The engineering of the Green Ring allowed for the population to expand into the thousands. As the first harvest of dwarf grain was brought in, Kael ordered the construction of Tier 8—the "Granary Tiers." The population count rose to 830 as a group of weavers and tailors from the northern foothills arrived, bringing with them the seeds for "Cavern-Flax," a fiber crop that could be grown in the Green Ring to provide the mountain with its own source of cloth.
Kael stood on the observation gantry of the Green Ring, looking down at the terraces of vibrant green light spiraling around the central geothermal core. The mountain was no longer a tomb or a fortress; it was a self-sustaining biosphere.
The cycle is nearly complete, Elms, Kael said, watching the Green-Keepers tend to the grain. We have the iron, the energy, the water, and now the bread. But a population of eight hundred needs more than just survival—it needs "Standardization." Our tools, our pipes, and our bolts are still made in dozens of different sizes. To reach five thousand, every part must be interchangeable. We need to start the Master-Gauge project.
Kael began the designs for a set of high-precision iron gauges that would define the "Ashfall Standard," ensuring that any part made in the foundry would fit any machine in the mountain, regardless of who forged it.