Sealing the barony within the limestone vaults of Outpost Alpha had solved the problem of physical vulnerability, but it had introduced a new, sensory crisis. To be underground was to be tactically blind. Kael could no longer rely on the Gray Fang's signal flags or the visual horizon to track the approach of the Imperial Ordnance Corps. To maintain the sovereignty of the barony, he needed a way to observe the surface without opening the twelve-ton blast doors. He initiated the development of the Seismic Mirror—a project that combined high-precision optics with the sensitivity of his earlier tremor-monitoring experiments.
The technical core of the system was a liquid-mercury pool positioned at the focal point of a large parabolic stone chamber. Kael utilized the surplus of mercury distilled from the lower-strata cinnabar deposits. This pool acted as a near-perfect reflective surface. By mounting the pool on a specialized isolation frame connected to the bedrock of the vault's ceiling, any vibration on the surface—the rhythmic march of a legion, the heavy roll of a siege engine, or even the movement of a scout—would create minute capillary waves on the mercury's surface.
Kael then projected a high-intensity beam of light from a bioluminescent concentrator onto the mercury pool. The reflected light was directed through a series of polished glass lenses onto a large, white-washed limestone wall in the central command vault. When the surface was still, the wall showed a perfect, unmoving circle of light. But when movement occurred above, the ripples on the mercury would distort the reflection, creating complex interference patterns that could be read like a visual map of the earth's movement.
The grit of the calibration was the translation of vibration into identity. Kael and the Information Citizens spent days "recording" the signatures of known movements. They had a team of oxen pull a heavy wagon over the surface to map the "Industrial Signature." They had the Tier 0 squad march in Imperial formation to record the "Military Rhythm." Every movement had a distinct frequency and amplitude, which translated into a specific visual "bloom" on the Seismic Mirror.
Socially, the command vault became the new heart of the barony. The Seismic Mirror was more than a tool; it was an oracle. The citizens would gather in silence to watch the wall, finding a strange comfort in the flickering light that connected them to the world they had left behind. The Analysts, now known as Mirror-Readers, developed a specialized intuition, able to distinguish between a natural rock-fall and the deliberate, measured approach of a sapper.
The technical failure occurred during a period of heavy sleet on the surface. The moisture from the freezing rain seeped into the upper ventilation shafts, causing a slight, constant "hiss" of vibration that blurred the mercury pool. The Seismic Mirror became a chaotic mess of white noise, rendering it useless just as the Gray Fang's last acoustic pipe signal warned of an approaching "Heavy Presence."
Kael didn't attempt to dry the shafts; he implemented the Differential Nullifier. He constructed a second, smaller mercury pool in a deep, isolated sub-vault that was immune to surface noise. By using a series of secondary lenses to "subtract" the noise of the sub-vault from the main mirror's projection, he was able to filter out the environmental interference. It was a mechanical version of noise-cancellation, allowing the true signal of the surface to emerge from the static.
The moment of clarity arrived on the first night of the new cycle. The Mirror-Reader on duty froze as the white-washed wall began to pulse with a slow, heavy, and perfectly synchronized vibration. It wasn't the oxen, and it wasn't the wind. It was the "Signature of Steel"—a massive, armored column moving in a wide-arc formation to encircle the outcrop.
Arch-Magister Vane had returned, and he hadn't brought a carriage. The Seismic Mirror showed the distinct, heavy bloom of Imperial heavy cavalry and the rhythmic, jagged spikes of mobile siege towers. The blockade had begun.
Kael looked at the glowing wall. The interference patterns were beautiful and terrifying, a visual representation of the force that meant to crush them. He looked at Elms, who was already coding the defensive response.
Vane is here, and he's brought the heavy iron, Kael said, his face illuminated by the flickering mercury-light. He thinks he's surrounding a mountain. He doesn't realize he's surrounding a machine that can feel his pulse through a hundred feet of stone.
Kael turned to the primary sluice-control. Close the upper vents. Switch the Thermal Accumulator to high-output. If they want to wait us out in the cold, we'll make sure the only thing they feel from this mountain is the heat of our defiance.