NEW YORK (AP) – The World Trade Center site fell silent four times as Americans paused in airport security lines, at churches and at quiet commemorations Monday to mark the fifth anniversary of the Sept. 11 terrorist attacks.

At ground zero, a cavernous pit still largely unchanged from the first anniversary, family members of the 2,749 people lost there held photos of loved ones, crossed themselves and sobbed quietly.

The 16-acre site went quiet at 8:46 a.m. and 9:03 a.m., the moments American Airlines Flight 11 and United Flight 175 hit, and again at 9:59 a.m. and 10:29 a.m., when the south and north towers fell.

“We’ve come back to remember the valor of those we’ve lost, those who innocently went to work that day and the brave souls who went in after them,” former Mayor Giuliani said.

Spouses and partners of the trade center victims read their names in a roll call that lasted nearly four hours, some adding brief personal tributes to their loved ones.

“Honey, I want you to have a happy grandparents’ day in heaven,” said Elaine Moccia, addressing her late husband, Frank Moccia Sr, as she released a balloon gently into the sky where the towers once rose 110 stories above the New York skyline.

President Bush opened the day at a historic New York firehouse, mingling with firefighters and police officers who were among the first to rush to the burning skyscrapers. He later laid a wreath on the Pennsylvania field where United Flight 93 crashed, and was to visit the Pentagon later in the day before giving a prime-time address from the Oval Office.

At ground zero, family members clutching bouquets of roses had descended to the lowest level of the trade center site, gathering around two small reflecting pools that marked where the two towers once stood.

The scene has played out on each of the five anniversaries of the Al Qaeda attack. And the landscape has remained mostly the same: Construction on a Sept. 11 memorial and on the 1,776-foot Freedom Tower began only this year.

“I think it’s important that people remember as years go on,” said Diana Kellie, of Acaconda, Mont., whose niece and niece’s fiance were killed on one of the planes. “The dead are really not dead until they’re forgotten.”

At the Pentagon, where 184 people died when American Flight 77 plowed into the building, Vice President Cheney and Secretary Rumsfeld walked side-by-side to a platform. They sang along to “Battle Hymn of the Republic” and observed a moment of silence at 9:37 a.m., the time the plane struck.

“We have no intention of ignoring or appeasing history’s latest gang of fanatics trying to murder their way to power,” Mr. Cheney said.

In Shanksville, where United Flight 93 crashed into the ground, killing 40, hundreds of people gathered at a temporary memorial _ a 10-foot chainlink fence covered with American flags, firefighter helmets and children’s drawings. They opened the ceremony with prayer.

United 93 crashed after passengers apparently rushed the cockpit in an effort to wrest control from the terrorists.

“These men and women stood in solidarity so others would receive salvation,” said Tom Ridge, former governor of Pennsylvania and the nation’s first homeland security secretary.

At Logan International Airport in Boston, where the two planes that hit the trade center towers took off, security screeners stopped checking passengers for a moment and turned to an American flag. Passengers in line joined in the silent tribute.

“It’s a difficult moment for everybody,” said National Guard Cpl. Christopher Jessop, who joined the Guard on Sept. 12, 2001.

In cities across the country, people stopped by churches to pray and remember the victims. In Virginia Beach, Va., firefighters and residents planned to form a human flag. In Ohio, volunteers aimed to put up 3,000 flags over 10 acres at a spiritual center. Kentucky officials marked the anniversary by rolling out a new computer system that will allow first responders to communicate from every corner of the state.

In Europe and around the world, heads bowed at Sept. 11 remembrances.

“Nine-eleven will be in our memory forever,” Rome Mayor Walter Veltroni said at a downtown piazza. “We all remember where we were, what we were doing, what our first reaction was.”

President Talabani wrote to President Bush, expressing condolences to the families of Sept. 11 victims: “On this sad and memorable day, I would like to reiterate the gratitude of the people of Iraq for the people of America.”

Chancellor Merkel, however, warned that “tolerance and respect for other cultures” must be hallmarks of the international fight against terror, and Prime Minister Clark said the world was not safer since 2001.

At the trade center site, Mr. Giuliani told ABC’s “Good Morning America” on Monday, “It took about 30 years for this terrorism to develop. It’s going to take more than five years to deconstruct them.”

“I’m kind of surprised at the progress we’ve made,” he said. “We haven’t been attacked in five years. I thought we would be. I thought for sure we would be. I thank God we haven’t. But we have to prepare for it.”

The anniversary dawned on a nation unrecognizable a half-decade ago _ at war in Afghanistan and Iraq, governed by a color-coded terror alert system, newly unable to carry even hair gel onto airplanes.

Bush administration officials had made the case Sunday it was no accident that the United States had not faced an attack since Sept. 11.

On the anniversary, there were indications of the tension that remains.

New York’s bustling Pennsylvania Station was briefly evacuated Monday and rush-hour train service was suspended when a suspicious bag was found. In the skies, a United Airlines jet headed from Atlanta to San Francisco was diverted to Dallas when an unclaimed BlackBerry e-mail device was found on board. A Transportation Security Administration spokeswoman later said the flight was secure.

There was also a fresh reminder of the terrorist threat: An hourlong videotape posted online Sunday showed previously unseen footage of Osama bin Laden, smiling, and other commanders apparently planning the New York and Washington attacks.

An unidentified narrator said the plot was devised not with computers and radar screens and military command centers but with “divine protection” for a brotherly atmosphere and “love for sacrificing life.”

Al-Jazeera aired a new videotape Monday in which bin Laden’s top deputy warned that Persian Gulf countries and Israel would be Al Qaeda’s next targets, and urged Muslims to intensify their resistance of the United States.

Mr. Bush had made a more private visit to the trade center site on Sunday, when he and first lady Laura Bush set wreaths in small, square reflecting pools in the pit of the trade center site, one for each tower.