A moment of silence was held at 9:37 a.m. - the time when hijacked Flight 77 crashed into the Pentagon ten years ago.
The country's political and military leadership was on hand at a ceremony to honor those who died in the terrorist attack, as well as those who responded in the moments that followed.
Between the personnel inside the Pentagon at the time of the attack and the passengers and crew aboard the plane, 184 victims perished that morning.
"I can say without fear of contradiction or being accused of exaggeration the 9/11 generation ranks among the greatest our nation has ever produced," Vice President Joe Biden told the assembled crowd. "And it was born, born, born right here on 9/11."
Biden recounted the heroism of the first responders that rushed forward to fight the flames in the moments following the crash. "Those that worked in this building, some of you in front of me, and thousands of other firefighters from Arlington County, Fairfax County, Montgomery County, the District of Columbia, and many others, they sprang to action," Biden said, "risking their lives so their friends and their comrades and total strangers, people they had never met, might live."
Defense Secretary Leon Panetta highlighted the contributions of the military in helping avert a repeat of the terrorist attacks. In his speech, he said more than 6,200 members of the U.S. military have died in the wars in Iraq and Afghanistan since the Sept. 11 attacks.
"The strength of our democracy has always rested on the willingness of those who believe in its values and there willing to serve and sacrifice for them, above all in times of crisis," Panetta said. "September 11th was such a time, and in the wake of the attacks, a generation of Americans stepped forward to serve in uniform, determined to confront our enemies and respond to them swiftly and justly."
President Barack Obama visited the Pentagon at 3:15 p.m. He laid a ceremonial wreath, and then greeted the family of victims who had gathered at the memorial.