September 11, 2001

It was a primary election day in New York City and an unusually clear late-summer morning on the eastern seaboard. The first impact was widely assumed, for about seventeen minutes, to have been a terrible accident.

The second aircraft hit the South Tower live on television. That is the moment the day changed from an accident into an attack, and it is the moment most people who were watching remember rather than the first.

By late morning the Federal Aviation Administration had ordered every civil aircraft in United States airspace to land — roughly 4,500 of them, at whatever airport could take them. Commercial flight did not resume for days.

American Airlines Flight 77 struck the western face of the Pentagon at 9:37 am, killing 125 people in the building and everyone aboard. A section of the outer ring later collapsed.

New York took most of the coverage that day and most of the memory since. The Pentagon is part of the same morning.

United Airlines Flight 93 was the last of the four to be taken and the only one that did not reach a target. Passengers and crew, who had learned from telephone calls what had already happened in New York, attempted to retake the aircraft.

It came down in a field near Shanksville at 10:03 am. Everyone aboard was killed. The intended destination was almost certainly Washington.

The Library of Congress's American Folklife Center began collecting almost immediately — not photographs of the attacks, but the things people put up afterwards. Handwritten signs, missing-person flyers, the walls of paper that appeared on fences and station tiles across New York.

Fragments of the towers were recovered and catalogued. The limestone below came from the World Trade Center facade.