Twenty-five years ago, on a crisp fall morning, four hijacked airplanes brought the United States into one of the darkest days in its history.

The attacks unfolded across New York, Virginia, and Pennsylvania, killing nearly 3,000 people and permanently changing American life. A quarter-century later, those three locations are preparing to commemorate the 25th anniversary of the 9/11 terrorist attacks with ceremonies honoring the victims, survivors, and first responders.