President Barack Obama and other top U.S. officials have paid tribute to the approximately 3,000 people who died in the September 11, 2001, attacks on the United States.
Speaking at a ceremony at the Pentagon, which was hit by one of the four hijacked airplanes, Obama remembered those who were killed and praised the strength of those who suffered losses and were able to pick themselves up and resume their lives.
"Your loved ones' everlasting place is in America's heart. We pray for you, their families who have known the awful depths of loss and in the quiet moments we spend together and from the stories that you've shared I am amazed at will that you've summoned in your lives to lift yourselves up, and to carry on, and to live, and love, and laugh again," Obama said.
"Even more than memorials of stone and water your lives are the greatest tribute to those that we lost, for their legacy shines on in you."
Defense Secretary Chuck Hagel also recalled the losses at the Pentagon that day. "Today we come together in honor of the fallen, surrounded by those who love them," he said.
"We remember each of those taken from us. We remember them as individuals with their own story. We comfort the loved ones they left behind who still mourn and grieve despite the passage of time."
The head of the U.S. Joint Chiefs of Staff, General Martin Dempsey, sounded a note of defiance, saying terrorism could not destroy the values that citizens of the United States embrace.
"No acts of terrorism can strike who we are; nothing can steal away that for which we stand," Dempsey said.
"So today, as we remember the 184 lives that ended here, the many who were injured and all who perished in New York and Somerset County, [Pennsylvania], let us hold firmly to those values for which they believed and for which they lived -- the best of America -- its freedom, its responsibility, and its promise."
PHOTO GALLERY: 'Survivors' Stairs' And Other Mementos Of September 11
Two steel "tridents" recovered from the World Trade Center site after September 11, 2001, stand in the entry area of the Memorial Museum.
Construction continues around the last column of steel removed from the World Trade Center site in 2002.
The "Survivors' Stairs," on display in the museum, offered an escape onto the street from the World Trade Center Plaza, becoming a symbol of survival for hundreds of people.
A message is seen on the bottom of the "Cross," intersecting steel beams found in the rubble of 6 World Trade Center.
Steel facade segments, also known as "Impact Steel," that were torn apart when hijacked United Flight 175 struck the South Tower of the World Trade Center on September 11, 2001.
The burnt-out cab of a New York City Fire Department (FDNY) fire truck is seen inside the Memorial Museum.
A portion of the original steel footings embedded in the bedrock for the South Tower of the World Trade Center
A construction worker walks past two steel "tridents" recovered from the World Trade Center site after September 11, 2001, in the entry pavilion area of the new museum.
A message from a recovery worker appears on the wall inside the Memorial Museum.
The "Cross" (left), intersecting steel beams found in the rubble of 6 World Trade Center, and a fragment of a trident column that formed the exterior structure of the World Trade Center buildings
Steel from the wreckage of the September 11 disaster. Workers at the site have cut shapes out of the discarded steel to give as mementos to other workers and victims' loved ones.
Visitors to the September 11 Memorial Plaza peer through the windows of the Memorial Museum.
A ceremony was also held in New York at the site where the twin towers of the World Trade Center once stood. Bells tolled and the names of the people who were killed were read aloud, in what has become a tradition on the anniversary of the attacks.
A similar ceremony was held at Shanksville, Pennsylvania, where one of the planes crashed, apparently after passengers overpowered the hijackers.
The United States ascertained Osama bin Laden and his Al-Qaeda terrorist network, at the time headquartered in Afghanistan, was to blame for the attacks.
The U.S. and allies launched an attack on Afghanistan before the end of 2001 that drove the Taliban from power but marked the start of war on insurgents that continues to this day.
Bin Laden was killed in Pakistan in 2011 by an elite U.S. commando team.
With reporting by Reuters, AFP, and AP