Flags are flying at half-staff today, Sept. 11, across California and the United States for Patriot Day.
Twenty-five years ago, on Sept. 11, 2001, terrorists launched an attack on American soil, killing almost 3,000 people in New York City, Washington, D.C., and in a Pennsylvania field.
"In just a little over two hours on Tuesday, Sept. 11, 2001, 2,977 innocent souls perished in the most despicable act of terror in the history of our country," President Trump said in a proclamation issued Sept. 9.
Patriot Day honors the memory of those victims and the first responders and service members who served after the attacks, especially for a generation who weren't even born when the attacks occurred.
On Sept. 11, 2001, the worst terrorist attack in U.S. history killed 2,977 people in New York City, Washington, D.C., and in a Pennsylvania. Tens of thousands of survivors and first responders still deal with 9/11-related health issues today.
Terrorists hijacked four passenger planes. Two planes crashed into two towers at the World Trade Center in New York City and a third crashed into the Pentagon outside Washington, D.C.
The fourth plane crashed into an empty field in Shanksville, Pennsylvania, after passengers tried to take control of the plane from hijackers before the plane was used to crash into another "important symbol of democracy and freedom."
In December 2001, a law was passed to designate Sept. 11 as Patriot Day. The law requests the president to issue a proclamation calling on:
Everyone to observe a moment of silence to honor those who were killed.
All state and local governments to observe Patriot Day with programs and activities.
Everyone to fly the U.S. flag at half-staff in honor of those who lost their lives on Sept. 11, 2001.
Related: From LA to Sacramento: Where to find 9/11 memorials across California
In a proclamation issued Sept. 9, President Trump issued a proclamation for the flag to be flown at half-staff on Sept. 11 "in honor of the 2,977 victims" who lost their lives in 2001.
"A quarter of a century has passed since the terrible day of Sept. 11, 2001, and an entire generation of Americans has now come of age with no living memory of that fateful day," Trump said.
"The passage of time must never dim what will forever burn bright in the conscience of our Nation. Amid the ashes of Ground Zero, we made a solemn vow to Never Forget — a vow that must be renewed in every American heart, taught in every classroom, and honored in every community across our land.
"Twenty-five years ago, beneath a clear September sky, the peace of our Nation was shattered when radical Islamic terrorists hijacked four commercial jet planes and converted them into weapons of mass murder."
The U.S. flag should be flown at half-staff across the country at all governmental buildings today, Sept. 11, in observance of Patriot Day.
No. Patriot Day is not a federal holiday. Government offices will be open, and mail will be delivered.
On days when the flag is flown at half-staff, it should first be raised to the top of the pole for an instant and then lowered to the half-staff position, according to the U.S. Flag Code.
Before lowering the flag, it should again be raised to the top before being lowered for the day.
On ships and at naval stations ashore, flags are flown at half-mast.
On shore, flags are flown at half-staff.
This story has been updated with new information.
This article originally appeared on Palm Springs Desert Sun: Why California flags are at half-staff today on Patriot Day