An American flag is seen in the plaque of names on the edge of the South Pool of the 9/11 Memorial in New York, Sept. 9, 2014. People will mark the 13th anniversary of the Sept. 11, 2001 terrorist attacks Thursday. Reuters

Thirteen years ago, on the early morning of Sept. 11, 2001, 19 al-Qaeda terrorists hijacked four passenger airliners and redirected the course of modern history. Two of those planes, American Airlines Flight 11 and United Airlines Flight 175, were flown into the north and south towers of the World Trade Center complex in New York City; 37 minutes later, American Airlines Flight 77 smashed into the Pentagon. At 10:07 a.m., United Flight 93 went down in a field in Pennsylvania.

The attacks that killed nearly 3,000 people ushered in a new era of homeland security and launched more than a decade of war. Sound bites – some intentional, some spontaneous and some pulled from cellphone records – from that day and the days that followed are reminders of the confusion, fear and horror that characterized 9/11. The words of world leaders, the deceased and those who survived are part of the historical significance of that day.

Here are some of the more memorable quotes from 9/11 and its aftermath.

The World Trade Center in New York City, Sept. 11, 2001. Both towers were hit by planes crashing into the buildings, and they collapsed a short time later. Reuters

During the attacks
“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.

Accompanied by Secretary of Defense Donald Rumsfeld, left, President George W. Bush speaks in front of the west side of the Pentagon Sept. 12, 2001 where terrorists plunged an airliner early Tuesday, Sept. 11. Reuters

Day of the attacks
"This mass terrorism is the new evil in our world today. It is perpetrated by fanatics who are utterly indifferent to the sanctity of human life, and we, the democracies of this world, are going to have to come together and fight it together." - British Prime Minister Tony Blair.

"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.” - U.S. President George W. Bush.

"We completely condemn this very dangerous attack, and I convey my condolences to the American people, to the American president and to the American administration, not only in my name, but on behalf of the Palestinian people." - Palestinian President Yasser Arafat.

"Commending the victims to almighty God's mercy, I implore his strength upon all involved in rescue efforts and in caring for the survivors." - Pope John Paul II.

“We’re going to find out who did this and we’re going after the bastards.” - Sen. Orrin Hatch, R-Utah.

A New York City fireman calls for more rescue workers to make their way into the rubble of the World Trade Center Sept. 15, 2001. U.S. President George W. Bush said September 17, 2001 he wanted Osama bin Laden "dead or alive" for the attacks that killed nearly 3,000 people. Reuters

Since the attacks
“What separates us from the animals, what separates us from the chaos, is our ability to mourn people we’ve never met.” – Author David Levithan in his book “Love is the Higher Law.”

"I may never be normal again. But this is my life now. I have to live it." - Manu Dhingra, 27, a securities broker who suffered burns over a third of his body but was released from the hospital Oct. 2, 2001.

“Remember the hours after Sept. 11 when we came together as one…It was the worst day we have ever seen, but it brought out the best in all of us.” – Then-Sen. John Kerry, D-Massachusetts, in 2004.

“Sept. 11, 2001 seems destined to be the watershed event of our lives and the greatest test for our democracy in our lifetimes.” – Lt. Col. Shelton F. Leskford, U.S. Marine Corps in 2008.

“'Most of the time it was even - right in line with the window we were staring out of. Then it was almost on us. I could make out the seams on the wings and all the American Airline markings. 'I looked right into the cockpit but I couldn't really make out the figures. They were tiny windows and the sun was shining on them. Maybe I eyeballed Mohammed Atta, the hijack pilot, but I can't be sure.'” – Survivor Fred Eichler.

“Ten years have passed since a perfect blue sky morning turned into the blackest of nights. Since then we’ve lived in sunshine and in shadow, and although we can never unsee what happened here, we can also see that children who lost their parents have grown into young adults, grandchildren have been born and good works and public service have taken root to honor those we loved and lost.” – New York Mayor Michael Bloomberg, speaking at a memorial service in New York.

“My son, firefighter Leon Smith Jr., who was the sunshine of my life. He gave his life so that others could live. I love you, I miss you and we’ll meet again soon.” – Irene Smith, whose son was a member of the Fire Department of New York Ladder Co. 118, speaking at a memorial service in New York.

“Five years from the date of the attack that changed our world, we’ve come back to remember the valor of those we lost—those who innocently went to work that day and the brave souls who went in after them. We have also come to be ever mindful of the courage of those who grieve for them, and the light that still lives in their hearts.” - New York City Mayor ­Rudolph Giuliani at the World Trade Center site in 2006.

“We join with our fellow Americans in prayer for the killed and injured.” – Imam at the Al-Abidin mosque in Queens, speaking to his congregation.

“I really believe that the pagans, and the abortionists, and the feminists, and the gays and the lesbians who are actively trying to make that an alternative lifestyle, the ACLU, People for the American Way–all of them who have tried to secularize America–I point the finger in their face and say, ‘You helped this happen.’” – Jerry Falwell, a Southern Baptist pastor and televangelist, in an appearance on Pat Robertson’s “The 700 Club.”

“Even the smallest act of service, the simplest act of kindness, is a way to honor those we lost, a way to reclaim that spirit of unity that followed 9/11.” - President Barack Obama in a 2011 radio address.