The eighty-ton keystone did not fall alone.
When the central eight-sided plug slipped from its seat at the apex of the dome, the inward crushing thrust of the eight huge granite stone props had nowhere to go. The balanced balance that had held thousands of tons of stone suspended over the Grand Round hall for twelve thousand years dissolved in a fraction of a split second.
The eight massive stone ribs splayed outward by two inches, their upper ends groaning like dying titans.
Without the keystone to wedge them into squeezing, three thousand cubic paces of outward cut stone vaulting—massive blocks of black dark rock and crystal-clear hard speckled rock weighing between four and twelve tons apiece—snapped along their bedding joints and peeled away from the ceiling like the rind of an opened pomegranate.
The collapse was an avalanche of cosmic proportions.
Eighty arm-lengths above the floor, eighty tons of solid black dark rock dropped into the center of the hall, followed right away by an avalanche of two thousand four hundred tons of falling ceiling stonework, carved roof ledges, and shattered bronze bells.
The sound of the falling stone was not a roar. It was a screaming, bone-shaking tear in the fabric of the air. A shifted weight of sixty million cubic feet of air that created a downward hurricane moving at ninety-six feet per second.
