As the drama was unfolding over the skies of Pennsylvania, one of the symbols of New York City disappeared from its skyline. Tower Two, the second tower hit by the hijacked airplane, collapsed. Thousands of people—office workers, firefighters, delivery workers, visitors, and others—were still inside the building when the beams supporting the upper stories buckled due to the fires' intense heat and were no longer able to support the weight. The tower pancaked. As one story fell, the floor below it was unable to support the additional weight, causing it to collapse, and so on and so on, until nothing was left of the building but a roiling cloud of gray dust. Barton Gellman, a correspondent for the Washington Post, was in New York City and witnessed the tower's disintegration into smoke and rubble:

Everything got all mixed...