Twenty-one years ago today, 9-11-2001, our country was viciously attacked by a coordinated terrorist plot that took lives, destroyed buildings, and left a mark on your hearts. Today, we remember those whose lives were lost.

As curated by Encyclopaedia Britannica, see below for a quick summary of this day of remembrance:

Patriot Day

A holiday observed in the United States of America on September 11 to commemorate the lives of those who died in the 2001 terrorist attacks on the World Trade Center in New York City and the Pentagon in Virginia and those who perished when the hijacked United Airlines Flight 93 crashed in Pennsylvania. The holiday also recognizes those who died attempting to rescue people trapped by the attacks.

By a joint resolution of the U.S. Congress on Dec. 18, 2001, September 11 was designated as Patriot Day. The resolution calls for the president of the United States to issue a yearly proclamation requesting that all U.S. flags be flown at half-staff. Further, Americans are asked to honor the dead with a moment of silence beginning at 8:46 AM, Eastern Standard Time, the time that the first airplane struck the World Trade Center, and to respect the ceremonies of remembrance when they are conducted. Prior to the passage of the resolution, several other names had been proposed for the day, such as the National Day of Remembrance and the National Day of Prayer and Remembrance.