The Pentagon, one of the three plane crash sites in the 9/11 terror attacks, observed on Monday the event's 5th anniversary with a solemn ceremony attended by several hundred government officials and family members of the victims.
U.S. Vice President Dick Cheney said in a speech at the ceremony that "we remember all that we saw and heard and felt on that Tuesday morning, and also how much the world changed on the 11th of September, 2001."
"It is a day of national unity. The memories stay with all of us because the attack was directed at all of us," he said.
Citing examples of how Pentagon staff members reached to one another's help on that day, Cheney, a former Defense Secretary, praised the "culture of Pentagon."
Five years after 9/11 have defined Pentagon's mission, he said, and that is, "--to defend America against a present danger and to offer a democracy and hope as the alternative to extremism and terror."
U.S. Defense Secretary Donald H. Rumsfeld appeared to have sobbed when he began to speak.
"Today we remember all of those who lost their lives, not only on September 11th, but in the struggle we have faced against extremists now for more than two decades," he said.
The highest tribute paid to the victims and fallen soldiers, Rumsfeld noted, is to "commit ourselves to doing everything possible to fight the extremists wherever they are."
Joint Chiefs of Staff Chairman Peter Pace said that the 2.4 million members of the U.S. military "have one very simple message for terrorists -- not on our watch."
A moment of silence was observed at 9: 37 a.m., the exact time five years ago when American Airlines Flight 77, traveling from Washington Dulles International Airport to Los Angeles, smashed into the west side of the Pentagon after being hijacked, killing 184 people.
On Saturday, some 1,000 people from all over the world took a tour of the Pentagon to honor the victims, marking only the second time the crash site has been made available to the general public since the 9/11 attacks.
Close to the site, a memorial park covering 0.8 hectares is under construction.
The Pentagon Memorial park will feature benches set over small reflecting pools commemorating each of the victims.