The seventh hour was the hour the Threian center broke.
Not bent. Not buckled. Broke. The specific structural failure that infantry formations produced when the formation's ability to absorb casualties was exceeded by the casualty rate that the formation was absorbing, the failure that occurred when the soldiers stepping forward to fill the gaps left by the dead and wounded ran out of soldiers to step forward with because the rear ranks had been consumed by the thundermaker fire that had been falling on the formation for seven hours.
