Family members clutching roses and bearing photos of the relatives they lost on Sept. 11 (search) fell silent early Saturday to mark the third anniversary of the World Trade Center attack (search).

Parents and grandparents of victims began reading the names of the 2,749 people lost in the trade center attack -- a recitation that was expected to take more than two hours.

"A man who loses his wife is a widower. A woman who loses her husband is a widow," Mayor Michael Bloomberg (search) said. "There is no name for a parent who loses a child, for there are no words to describe this pain."

The first moment of silence was observed at 8:46 a.m., the time American Airlines Flight 11 slammed into the center's north tower on Sept. 11, 2001. Another moment was held at 9:03, the time of the second plane crash; similar moments were planned for 9:59 and 10:29 a.m., when the towers collapsed.

As the nation began a day of remembrance, the president and first lady also presided over a moment of silence on the White House's South Lawn.

Pat Hawley, of Charlotte, N.C., said he comes to the ground zero ceremony every year to remember his older sister, Karen Sue Juday.

"It seems like it gets harder every year, because it's that much more time since I've been able to talk to my sister and be with her," said Hawley, 44.

There were roses available for family members to pick up as they came in.

Nancy Brandemarti, who has never attended the ground zero remembrance, will read a poem for her son, Nicky Brandemarti, a financial analyst who died just weeks before his 22nd birthday.

"Every day is hard, but this day is a little bit harder," she said. "This day is just a day to think about him."

At the Pentagon, where 184 people were killed that day by another hijacked plane, officials were to lay a wreath and observe a moment of silence. In Pennsylvania, bells will toll across the state at the minute the fourth plane went down, killing the 40 passengers and crew killed aboard Flight 93.

Nationwide, communities will observe Sept. 11 in their own ways, with services at local firehouses, memorial dedications, bell-ringing events and flag ceremonies.

On the first anniversary of the attacks, dignitaries, community leaders and relatives of victims stood at ground zero and gave voice to the names of the dead. Last year, the children of victims took up that task.

Bloomberg's predecessor, Rudolph Giuliani, New York Gov. George Pataki and New Jersey Gov. Jim McGreevey were also expected to deliver readings.

During the ceremony, families will be able to walk down a ramp to the footprints of the towers. The area, seven stories below street level, is considered sacred ground by many. It was there that rescue workers combed the debris with rakes, painstakingly searching for the tiniest fragments of human remains.

Three years later, work still continues to identify the 20,000 pieces of human remains that were recovered. The medical examiner's office has identified about 1,570 victims, or just 60 percent. They do not expect to match the remains of every victim because some remains were too badly damaged to yield readable DNA, and some people were essentially vaporized in the fiery collapse.

Meanwhile, much has changed at the 16-acre site.

By the first anniversary, the debris of the 110-story towers had been cleared, but there was little activity there other than construction that had begun to replace commuter train tracks. By the second anniversary, the train station was nearly complete, and it opened last November.

The redevelopment of the site has seen another major step in the last year -- the laying of the cornerstone for the 1,776-foot-tall Freedom Tower, the skyscraper expected to be completed by 2009. The 20-ton slab of granite was laid at the site in a July 4 ceremony this summer.

Victims were to be honored at several other events in New York City on Saturday, including a Mass at St. Patrick's Cathedral for fallen firefighters and the dedication of a memorial to Staten Island victims at the ferry terminal across the harbor from the trade center site.

At sundown, light beams that evoke the twin towers will be projected upward from a lot near the site, to remain on through the night. The memorial lights were first seen on March 11, 2002, to mark six months since the attack, with a plan to light them each year for the anniversary.