Patriot Day is observed every year as the National Day of Service and Remembrance to honor those who died in the Sept. 11, 2001, terrorist attacks.

It’s been 19 years since 9/11, the most devastating attack to hit the United States. Nearly 3,000 people died in the assault, which was carried out by al Qaeda terrorists. On Sept. 11, 2001, hijackers seized four passenger planes and crashed them into the north and south towers of the World Trade Center in New York City, the Pentagon in Virginia and a field in Pennsylvania.

Here are some quotes from during the attack:

“What do I tell the pilots to do?” -- Barbara Olson, CNN commentator and a passenger on American Airlines Flight 77 during a cellphone call to her husband, Solicitor General Theodore Olson.

“We have some planes. Just stay quiet and you will be okay. We are returning to the airport. Nobody move, everything will be okay. If you try to make any moves you'll endanger yourself and the airplane.” -- Mohamed Atta, American Airlines Flight 11 hijacker pilot, heard on a radio transmission while intending to send a message to the passengers.

“Something is wrong. We are in a rapid descent... we are all over the place. ... I see water. I see buildings. We are flying low. We are flying very, very low. We are flying way too low. ... Oh my God, we are way too low... Oh my God, we're —” -- Flight attendant Madeline Amy Sweeney describing the hijacking of American Airlines Flight 11 at the end of her phone call to a supervisor.

"Are you guys ready? Let's roll." -- Flight 93 passenger Todd Beamer, apparently as a signal to other passengers to attack the hijackers.

"We're young men; we're not ready to die." -- Kevin Cosgrove, a business executive who was on the 105th floor of the south tower moments before it collapsed.

"Hi, this is the captain. I would like you all to remain seated. There is a bomb on board and we are going back to the airport ... Please remain quiet." -- hijacker aboard United Flight 93, which crashed near Shanksville, Pennsylvania.

"We may have a hijack. We have some problems over here right now." -- air traffic controller on the ground on Long Island shortly after the first plane struck the north tower.

"Numerous civilians in all stairwells, numerous burn [victims] are coming down. We're trying to send them down first… We're still heading up.” -- Capt. Patrick Brown, whose company had climbed to the 35th floor of the north tower a half-hour before the first collapse.

Here are some quotes from after the attack:

"The number of casualties will be more than most of us can bear." -- then-New York City Mayor Rudolph Giuliani.

“Today, our fellow citizens, our way of life, our very freedom came under attack in a series of deliberate and deadly terrorist acts. The victims were in airplanes or in their offices: secretaries, business men and women, military and federal workers, moms and dads, friends and neighbors. Thousands of lives were suddenly ended by evil, despicable acts of terror. The pictures of airplanes flying into buildings, fires burning, huge -- huge structures collapsing have filled us with disbelief, terrible sadness and a quiet, unyielding anger. These acts of mass murder were intended to frighten our nation into chaos and retreat. But they have failed. Our country is strong. A great people has been moved to defend a great nation.” -- George W. Bush.

Smoke pours from the twin towers of the World Trade Center after they were hit by two hijacked airliners in a terrorist attack in New York City, Sept. 11, 2001. Getty Images/ Robert Giroux