"As painful as this day is and always will be, it leaves us with a lesson: that no single event can ever destroy who we are, no act of terrorism can ever change what we stand for," the president said at a memorial ceremony at the Pentagon. "Instead, we recommit ourselves to the values that we believe in, holding firmly, without wavering, to the hope that we confess."
Recalling a day "that began like so many others," the president said, "It is easy for those of us who lived through that day to close our eyes and to find ourselves back there and back here, back when grief crashed over us like an awful wave, when Americans everywhere held each other tight, seeking the reassurance that the world we knew wasn't crumbling under our feet."
Since the terrorist attacks that killed nearly 3,000 people, the president said America has "dealt a crippling blow to the organization that brought evil to our shores."
"Al Qaeda's leadership has been devastated, and Osama bin Laden will never threaten us again," said Obama, who also cited the end of the Iraq war and the transition in Afghanistan.
The president assured the victims' families that "no matter how many years passed, no matter how many times we come together on this hallowed ground, know this, that you will never be alone."
"Your loved ones will never be forgotten. They will endure in the hearts of our nation because through their sacrifice, they helped us make the America we are today, an America that has emerged even stronger," he said.
After his remarks, the president and first lady spent close to an hour greeting the families of those who lost their lives in the attacks.
On their way back to the White House, the president and Mrs. Obama stopped at Arlington National Cemetery, where they visited the graves of service members killed in Iraq and Afghanistan.