For the first time, elected officials did not speak at the ceremony in New York.
"I feel much more relaxed" this year, said Jane Pollicino, who came to ground zero Tuesday morning to mourn her husband, who was killed at the trade center. "After the ninth anniversary, that next day, you started building up to the 10th year. This feels a lot different, in that regard. It's another anniversary that we can commemorate in a calmer way, without that 10-year pressure."
Eleven years later, the World Trade Center again dominates New York City's skyline. The One World Trade Center tower was formerly known as the Freedom Tower. It remains under construction and is set to open in 2014.
Bagpipes played at the year-old Sept. 11 memorial, as the crowd bowed their heads in silence at 8:46 a.m., the moment that the first hijacked jetliner crashed into the trade center's north tower. Bells tolled to mark the moments that planes crashed into the second tower, the Pentagon and a Pennsylvania field, and the moments that each tower collapsed.
"The 11th year, for me, it's the same as if it happened yesterday," said Joe Torres, whose sister-in-law was killed in the attacks. "It could be 50 years from now, and to me, it'll be just as important as year one, or year five or year ten."
Mayor Michael Bloomberg, Gov. Andrew Cuomo, New Jersey Gov. Chris Christie and former Mayor Rudy Giuliani all attended the ceremony.
Like 2001, this Sept. 11 was on a Tuesday, and the early fall weather was eerily similar to the morning on 2001.
President Barack Obama and first lady Michelle Obama observed the moment in a ceremony on the White House's south lawn, and then laid a white floral wreath at the Pentagon, above a concrete slab that said "Sept. 11, 2001 - 937 am."
Mr. Obama recalled the horror of the attacks, declaring, "Our country is safer and our people are resilient."
Victims' families also gathered near Shanksville, Penn., where United Flight 93 came down. They rang bells of remembrance for the 40 passengers and crew members who died there. Lanterns were also placed in their honor at the memorial. Vice President Joe Biden and Secretary of the Interior Ken Salazar were on hand to speak. Secretary of Defense Leon Panetta stopped there on Monday to get a private tour of the Flight 93 National Memorial.
"We cannot forget that sacrifice, because in many ways, it is what makes America strong. It's what we are about," said Panetta. "It's the spirit that was reflected in the heroes here, who were willing, on a plane, to suddenly charge ahead knowing that it was very likely that they were giving their lives for their country."
The September 11 Memorial & Museum in lower Manhattan was supposed to open this month, but a funding squabble delayed construction. On Monday, the museum's foundation and the port authority reached an agreement on the funding, and construction is expected to continue. An eight-acre memorial, featuring reflecting pools where the towers stood, opened last year on the 10th anniversary.
People from all over the country are coming together to remember the victims of the attacks. See a list of ceremonies taking place in Southern California.