Twenty-five years have passed since the terrorist attacks of Sept. 11, 2001, but the lives lost and the actions of those who responded continue to be remembered.

     That morning, terrorists hijacked four commercial airplanes. Two struck the World Trade Center towers in New York City, one crashed into the Pentagon and another crashed near Shanksville, Pennsylvania, after passengers and crew members attempted to regain control.

     The attacks killed 2,977 people, including passengers, office workers, military personnel and first responders.

     Many who worked in the rescue and recovery efforts later developed illnesses linked to hazardous conditions at the World Trade Center site.

     The attacks also changed life across the United States. Airport security increased, new federal security measures were enacted and American military forces were sent overseas.

     Native American service members were among those who served during the wars that followed.

     For younger generations, Sept. 11 is now an event learned about through classrooms, photographs and stories from relatives.

     The anniversary is observed as Patriot Day and the National Day of Service and Remembrance. Flags are flown at half-staff, memorial ceremonies are held and Americans are encouraged to honor the day through service.

     As the country marks the 25th anniversary, the day remains an opportunity to remember those who were lost, recognize those who responded and reflect on the unity shown afterward.