Moments of silence were held across America Thursday morning to mark the devastating events of the Sept. 11 attacks (search), two years ago to the day.

The nation went silent at 8:46 a.m. and again at 9:02 a.m. and 9:37 a.m. to remember the moments when terrorists flew three planes into the World Trade Center (search) and the Pentagon (search). At 9:59 a.m., the time when the trade center's south tower fell, and at 10:28 a.m., when the north tower fell, two more moments of silence were held.

In Shanksville, Pa., rural hamlets tolled bells 40 times to mark 10:06 a.m., the time when United Flight 93, the fourth hijacked plane, plunged into a field there, killing the 40 passengers and crew. A small crowd of families gathered at the field.

• Photo Essay: Remembering 9/11

A total of 3,016 people were killed in New York, Washington and Pennsylvania.

Two bagpipers and a drummer marched to the former site of the World Trade Center just before 8:46 a.m., bearing an American flag that once flew over the ruins.

The three men represented the Fire Department, the Police Department and Port Authority, which together lost more than 400 people.

"We come here to honor those that we lost, and to remember this day with sorrow," Mayor Michael Bloomberg said. A total of 2,792 people died in New York.

At 8:46 a.m., those gathered at Ground Zero (search) paused for the first moment of silence to remember when the first plane hit the north tower. A second moment of silence was held at 9:02 a.m. to remember when the second plane hit the south tower.

In between, 200 children whose relatives were among the thousands who died on Sept. 11 each began reading 14 victims' names in the main morning ceremony.

In Washington, President Bush and 2,000 White House staffers observed 8:46 a.m. at the White House.

"We remember the compassion, the decency of our fellow citizens on that terrible day," Bush said after a church service at St. John's Church. "We pray for the husbands and wives and moms and dads and sons and daughters of loved ones who still grieve and hurt."

He added: "We thank God for the many blessings of this nation and we ask his blessings for those who especially hurt today."

Meanwhile, Defense Secretary Donald Rumsfeld took part in a wreath-laying ceremony at Arlington National Cemetery in Virginia in observance of Patriot Day (search), the name given to Sept. 11 by presidential proclamation.

A moment of silence was observed at the cemetery and the Pentagon at 9:37 a.m., the time American Flight 77 crashed into the Pentagon and killed 184 people.

"Patriot Day is a day to remember them [Pentagon victims], as well as those who died in Pennsylvania and New York -- to remember their lives and their legacies," said Joint Chiefs of Staff Chairman Richard Myers. "We will not merely endure, we will prevail."

"We gather here today to honor the heroes who sleep in these hills and to commemorate the second annual observance of Patriot Day," added Rumsfeld. "Freedom will triumph over tyranny."

Memorials, Vigils and Healing

At Ground Zero, a chorus of children sang "America the Beautiful," "The Star-Spangled" Banner and a song called "The Prayer."

"I know I'm very proud of my children," said Lynn Morris, whose husband, Seth Allan Morris, died that day, and whose two children, 11-year-old Madilynn and 9-year-old Kyle, read names. "It's amazing the strength that they have developed over the years."

Morris looked up articles so her children could match faces to the names they were to read. Madilynn was reading her 14 names, finishing with that of her father, who was 35 and worked at Cantor Fitzgerald in the trade center.

"I thought it would be a good way to honor my dad," Madilynn said, "and to honor the other people."

Also in New York, a silent vigil was held Wednesday night at St. Paul's Chapel and continued into the early hours of Thursday morning.

The chapel, once in the shadow of the trade center, survived the neighboring complex's destruction and was temporarily converted into an all-purpose relief center for rescue workers.

Hundreds of Washington, D.C., students and school officials paused Thursday morning to remember classmates and teachers killed in the Pentagon attack. Three D.C. students and three teachers who died on that hijacked plane were on their way to a field trip in California.

In Toledo, Ohio, white doves were to be released after the reading of victims' names. In Massachusetts and Hawaii, bells pealed to remember the dead.

Twisted steel taken from the Ground Zero ruins and shipped to other states for memorials was to be at the center of ceremonies from North Dakota to Florida to a New Mexico church that uses two trade center beams as part of its bell tower.

In Kennesaw, Ga., more than 3,000 American flags were on display. In Missouri, a new granite memorial made with wreckage of the trade center was to be dedicated Thursday. Standing six-feet tall, it's inscribed with an image of Lady Liberty and a poem about the spirit of America.

And in Tampa, Fla., motorcycle riders were raising money for the families of police, firefighters and U.S. Special Operations troops who have died in the war on terrorism.

"It helps bring people together, and it helps us feel united," spokeswoman Elaine Diaz said.

The Ground Zero commemoration featured readings by Mayor Michael Bloomberg, former Mayor Rudolph Giuliani, New York Gov. George Pataki and New Jersey Gov. James McGreevey. New Jersey lost 700 people on Sept. 11.

"People are at very different stages of grieving," McGreevey told Fox News before the ceremony. "What we have to do is understand that this is affecting their lives every day."

Families of attack victims descended a ramp into the seven-story pit that was the trade center basement and placed flowers on the bedrock.

At sunrise Thursday, about 200 people gathered in quiet prayer at a waterfront park near where the twin towers once stood, and at sunset, two light beams pointing skyward will be switched on, evoking the image of the twin towers in a reprise of a popular monthlong memorial unveiled in March 2002.

"I don't know if we'll ever heal," said Roberto Brozen, 57, who lives near the southern tip of Manhattan. He said he was reminded of "how fragile we are and how important we are to each other."

The Associated Press contributed to this report.