The crack that split the upper dome did not sound like thunder.
Thunder was the violence of air and heat, transient and hollow, echoing through open skies before fading into nothingness. The sound that tore through the Grand Central Round hall was the shearing of ten thousand tons of native granite. A deep, underground tearing that travelled through the bedrock, shaking directly through the bones of every man in the tiered arena.
One hundred and twenty arm-lengths above the floor, the huge dark rock carving of the Primordial Tortoise dropped fourteen inches into its relief recess. The massive six-sided plates of its shell, interlocked for eight hundred years by friction and care stonework, buckled under the sudden release of five hundred deep-water lengths of water-pressure head.
The ceiling of the Grand Central Round hall was an inverted dome engineered by the Seventh Master during the Second Epoch. Rather than relying on crushing iron ties, the dome was built from forty-eight nested rings of dark fiery dark rock, each block shaped as a truncated wedge that sent the upright load outward into the twelve massive stone props of the mountain outer edge. For eight hundred years, the dome had carried not only the sky weight of the upper peaks. But an artificial lake containing forty million cubic arm-lengths of water, kept as an emergency dampening mass against fiery tremors.
