"That day we felt isolated, but not for long and not from each other," Mayor Michael Bloomberg said as the ceremony began. "Six years have passed, and our place is still by your side."
Construction equipment now fills the vast city block where the World Trade Center once stood. the work is under way for four new towers forced the ceremony to be moved away from the twin towers' footprints for the first time.
As people clutched framed photos of their lost loved ones, Kathleen Mullen, whose niece Kathleen Casey died in the attacks, said the park across the street was close enough.
"Just so long as we continue to do something special every year, so you don't wake up and say, 'Oh, it's 9/11," she said. Presidential politics and the health of ground zero workers loomed over the sixth anniversary of the terrorist attacks this year, perhaps more than any other Sept. 11.
The firefighters and first responders who helped rescue thousands that day in 2001 and later recovered the dead were to read the victims' names for the first time. Many of those rescuers are now ill with respiratory problems and cancers themselves, and they blame the illnesses on exposure to the fallen towers' toxic dust.
Also for the first time, the name of a victim who survived that towers' collapse but died five months later of lung disease blamed on the dust she inhaled was added to the official roll.
Felicia Dunn-Jones, an attorney, was working a block from the World Trade Center. She became the 2,974th victim linked to the four attack sites where hijacked airliners hit the two towers, the Pentagon and a field near Shanksville, Pa., where federal investigators say the passengers of United Airlines Flight 93 fought the hijackers on the rallying cry "Let's roll!"
A memorial honoring Flight 93's 40 passengers and crew was to begin at 9:45 a.m., shortly before the time the airliner nosedived into the empty field.
"The ceremony will be brief but solemn," said Kevin Newlin, an official with the National Park Service. Bells will toll, and the names of the passengers and crew will be read at the site of a temporary memorial at the crash site.
In Boston, where two of the hijacked airplanes took off that morning, church bells rang to the tunes of Amazing Grace and America the Beautiful on Tuesday.
In New York, drums and bagpipes played as an American flag saved from the collapse was carried toward a stage. Firefighters were to
share the stage with former Mayor Rudy Giuliani, who many victims'
families and firefighters said should not speak because he is running for president. Giuliani has made his performance in the months after the 2001 terrorist attacks the cornerstone of his campaign, but he has said his appearance wasn't intended to be political.
"I was there when it happened and I've been there every year since then. If I didn't, it would be extremely unusual. As a personal matter, I wouldn't be able to live with myself," Giuliani said late last week.
Sen. Hillary Rodham Clinton, seeking the Democratic Party presidential nomination, also planned to attend the ceremonies at ground zero.
President Bush, with the first lady at his side, held a moment of silence on the South Lawn of the White House. At the main U.S. base at Afghanistan, a memorial ceremony was also planned.
National intelligence director Mike McConnell said Tuesday that U.S. authorities remain vigilant and concerned about "sleeper cells" of would-be terrorists inside the United States.
"We're safer but we're not safe," McConnell said in an interview on ABC's "Good Morning America."
As in past years, moments of silence were planned to mark each
crash and the collapse of each tower in New York.
Even thought the World Trade Center ceremony gathering was in
the park, thousands of family members were still allowed to descend
briefly below street level to lay flowers at a spot near the twintowers' footprints. Family members upset that they might not be allowed in at all pressured the city to at least allow the short visits to the dusty bedrock.
In addition to the firefighters and first responders reading victims' names during the ceremoney, city workers who participated in the cleanup, construction workers, volunteers, and medical examiner's officials who recovered remains were involved.
In all, 2,974 victims were killed by the Sept. 11 attacks: 2,750 at the World Trade Center, 40 in Pennsylvania and 184 at the Pentagon. Those numbers do not include the 19 hijackers.