On September 11, 2001, under clear blue skies, 102 minutes changed the lives of Americans and people all over the world forever.

On this day 21 years ago—under clear blue skies—102 minutes changed the lives of Americans and people all over the world forever when 19 terrorists executed a coordinated attack on American soil, killing 2,977 people. On the morning of September 11, 2001, members of al-Qaeda hijacked four commercial airplanes, flying two of the planes into the Twin Towers of the World Trade Center, the third into the Pentagon, and the fourth crashing into a Pennsylvania field after passengers initiated a counterattack. The devastation resulted in 2,977 innocent lives lost, the single largest loss of life resulting from a foreign attack on American soil. Below is a timeline of events from September 11, 2001.

8:46 a.m.: American Airlines Flight 11 crashed into floors 93 through 99 of the North Tower in N.Y.C.
9:03 a.m.: United Airlines Flight 175 crashed into floors 77 through 85 of the South Tower in N.Y.C.
9:37 a.m.: American Airlines Flight 77crashed into the Pentagon, near Washington, D.C.
9:59 a.m.: The South Tower collapsed.
10:03 a.m.: Passengers on United Airlines Flight 93 learned of the other attacks on the Twin Towers and launched a counterattack on the hijackers. In response, the hijackers crashed the plane into a field near Shanksville, Pennsylvania
10:28 a.m.: The North Tower collapsed.

Millions witnessed the events of the day unfold, sharing the experience of horror and grief. Some were compelled to take action to help. The rescue and recovery efforts at the attack sites began immediately as volunteers from all over the world descended to New York, Pennsylvania, and D.C. Volunteers worked relentlessly in hazardous working conditions for months, searching for remains and clearing out debris from the wreckage. In times of tragedy, we came together to support one another. A sense of unity poured into our streets, towns, and cities.

Just a little over a month later, in October 2001, a bill was introduced to the U.S. House of Representatives to make September 11 a national day of mourning. The one-year anniversary of the attacks marked the first Patriot Day. President Barack Obama proclaimed September 11 as Patriot Day and National Day of Service and Remembrance (2009–2016). President Donald Trump proclaimed September 8–10 as National Days of Prayer and Remembrance, and proclaimed September 11 as Patriot Day (2017). We continue to keep our vow to never forget and embrace the sense of unity.

Every year on the anniversary of September 11, 2001, memorials and tributes are displayed throughout the United States. Each year, in New York City, at the World Trade Center, the names of the 2,983 victims of the September 11, 2001, and February 26, 1993 attacks are read out loud. Moments of silence are observed at the time of the attacks. In Pennsylvania and D.C, memorial ceremonies are held at the attack sites. Organizations like AmeriCorps and 9/11 Day provide opportunities to honor September 11, 2001 through volunteer work.

Today, we remember the 2,977 lives lost on September 11, 2001. We stand in solidarity with the families and friends of those who mourn and grieve. We salute the volunteers who selfishly give their time to those in need. We continue our promise to never forget September 11, 2001.

For more information on the history of September 11, 2001, visit The Library of Congress and the 9/11 Memorial & Museum.