WASHINGTON — First lady Jill Biden and the top two leaders at the Pentagon took time Monday to pause and honor the nearly 200 people who were killed 22 years ago at the building in the 9/11 terrorist attacks — and promised always to remember them as that day moves further into the past.

“As the years go by, it may feel that the world is moving on, or even forgetting what happened here,” Defense Secretary Lloyd Austin said Monday morning during a ceremony at the Pentagon’s 9/11 memorial. “But please know this: The men and women of the Department of Defense will always remember.”

The ceremony was one of three at the Pentagon in recent days. On Friday, a 9/11 ceremony was held specifically for department employees in the building’s center courtyard. Another took place Monday afternoon and included a wreath-laying ceremony with Biden.

“Twenty-two years ago, the horror of 9/11 changed us all,” she said. “We must always remember those lost that day and in the aftermath. We will keep their families always in our hearts. We stand with them today and every day.”

The attack at the Pentagon killed 184 people — 59 people on American Airlines Flight 77 and 125 people on the ground.

Pentagon officials unfurled an American flag over the side of the Pentagon on Monday, Sept. 11, 2023, at sunrise at an observance ceremony at the National 9/11 Pentagon Memorial to honor the 184 lives lost in the 2001 terrorist attack on the Pentagon. (Cesar J. Navarro/U.S. Air Force)

“September 11th reminds us that the American spirit still shines in times of testing. After the attacks, amid the horror and the grief, many Americans felt a deeper sense of duty to their communities and to their country,” Austin said. “September 11th made America a nation at war, and hundreds of thousands stepped up to serve our country in uniform. The wars in Iraq and Afghanistan have come to a close, but we remain relentlessly focused on combating terrorist threats to America.”

The Pentagon’s 9/11 memorial, opened in 2008, features 184 cantilevered benches — one for each person who died — on the southwestern side of the building near the spot where the hijacked airliner hit. Each bench is made of stainless steel and inlaid with smooth granite, and each one contains a pool of water that reflects light in the evenings.

The benches for those killed on the ground are arranged so their names and the Pentagon are aligned. For those who died aboard Flight 77, their names are aligned with the direction that the plane was traveling when it crashed.

Army Gen. Mark Milley, who will retire later this month as chairman of the Joint Chiefs of Staff, said Americans showed unequivocally that they will not be defeated by terrorism.

“Those terrorists hated America,” he said. “They hated our Constitution and the values that bind us together as a nation.”

“Those terrorists wanted to destroy our country, but on that day and every day since, the United States has demonstrated that we would never bow to fear and hatred,” Milley said.

Almost 3,000 people were killed in the 9/11 attacks — mostly at the World Trade Center in New York, where the towers were struck by planes that had been hijacked in Boston. The plane that hit the Pentagon was hijacked after leaving Washington Dulles International Airport in Virginia, and the final hijacked flight, United Airlines Flight 93 out of New Jersey, crashed near Pittsburgh after a passenger revolt prevented the terrorists from reaching their target, which was believed to be the U.S. Capitol.

Also in attendance Monday at the ceremony were Tu and An Nguyen, the wife and son of a Navy systems administrator who died in the attack at the Pentagon. An, who was just 4 at the time, is now 26.

“Twenty-two years later, Tu and An are incredibly close, and their tie has only grown stronger from the loss that they’ve endured,” Austin said. “I want to thank them, and all of the families of the fallen.”

“In so many ways, you turned grief into grit and sorrow into strength,” he added. “So, it is our duty to carry out the missions that your loved ones chose. It is our duty to live up to the goodness that they embodied. And it is our duty to defend the democracy that they loved so much.”

President Joe Biden made public remarks on the anniversary of 9/11 from Anchorage, Alaska, while on his way back to Washington from a G20 summit in India and a trip to Vietnam.

“I join you on this solemn day to renew our sacred vow: Never forget … we never forget,” Biden said at Joint Base Elmendorf-Richardson. “Each of those precious lives [were] stolen too soon when evil attacked.”

“I remember standing there [at Ground Zero in New York] the next day … I felt like I was looking through the gates of hell,” said Biden, who was the senior senator from Delaware at the time of the attacks. “It’s more important than ever that we come together around the principle of American democracy, regardless of our political backgrounds.”

Also commemorating the 22nd anniversary of the attacks, the Smithsonian Institution has placed a fire truck — the first to respond at the Pentagon — on display at the National Air and Space Museum’s Steven F. Udvar-Hazy Center in Chantilly, Va. The “crash truck,” known as Foam 331, later was stationed at Dulles International Airport until its retirement in 2016. After being used by a Canadian company for a few years, it was returned to its manufacturer and restored to its 2001 appearance.

“We are really honored to be able to present the vehicle,” Roger Connor, the Smithsonian’s curator of aeronautics, said. “The ability to tell a more comprehensive 9/11 story is essential for acknowledging and commemorating one of the most traumatic moments in our nation’s history.”

The museum said it will hold a formal dedication for the truck in 2026 at about the time of the 25th anniversary of 9/11.