From New York City and Washington, D.C., to the small town of Shanksville, Pa., the first Memorial Day after the Sept. 11 terrorist attacks took on a renewed sense of meaning and a particularly somber tone.

The thousands who died that day and during the subsequent war in Afghanistan were the focus of many ceremonies across the country Monday on a national holiday that over the years had become little more than a kick off to the start of summer.

In New York City, a ceremony honoring the 3,000 who died in the World Trade Center collapse was held near the site of the destruction, now known as Ground Zero.

New York Mayor Michael Bloomberg dropped a wreath into the Hudson River to honor Americans who lost their lives in times of war.

Hundreds of veterans observed a moment of silence aboard the Intrepid Sea Air Space Museum after a chaplain blessed the military for protecting America.

As fighter jets flew overhead, a new flag was unfurled to replace one that was placed atop the American Express building near Ground Zero. The same team of fighter jets had flown missions into Afghanistan from the USS Enterprise last fall.

In Arlington National Cemetery outside Washington, D.C., the U.S. military paid homage to the 9/11 and other fallen heroes during the traditional wreath-laying ceremony at the Tomb of the Unknowns.

Deputy Secretary of Defense Paul Wolfowitz took part in the event.

"We face another hour of great testing and yes, liberty — our way of life — is once again in peril," said Wolfowitz. "I've long believed that America's greatest power ... is what it stands for."

At a separate remembrance at the wall built for America's Vietnam War victims, former Sen. Bob Dole called on the nation to win the war on terrorism and declared "we were underestimated on Sept. 11."

Other military observances took place at U.S. bases across the country, at deployed locations in foreign countries, and on all ships at sea. The commander of U.S. forces in Afghanistan, Gen. Tommy Franks, urged Americans to remember those making special sacrifices in the war on terrorism.

And in Shanksville in western Pennsylvania, scores of people visited the field where United Airlines Flight 93 crashed after an apparent struggle between hijackers and passengers.

Ernie Philips, 38, a U.S. Navy commander from Woodbridge, Va., who was in the Pentagon when it was struck by another hijacked jet, stopped at the crash site near Shanksville, Pa., with his wife and two children during a trip home from Ohio.

"These folks, in my mind, saved so many lives," said Philips, standing by a chain-link fence draped with flags, poems and flowers. "They were on the front line. The enemy was right there."

Army veteran Jay Brunot, 67, and his wife, Jean, 66, a registered nurse, traveled to the site after attending a holiday parade in Latrobe, about 40 miles away.

"The whole day is supposed to be a recognition of those who died to protect us," Jay Brunot said. Flight 93 passengers, his wife added, "were just as important as the veterans were."

Other Sept. 11 victims were remembered in smaller memorial events around the nation.

About 150 residents gathered in a light rain on the town green in Burlington, Mass., to dedicate a memorial to three men with ties to the Boston suburb who were aboard American Airlines Flight 11 when it struck the World Trade Center.

"Evil tried to obliterate us, but it didn't. The World Trade Center may have been struck down, but we were not destroyed," said Cheryl McGuinness, whose husband, Thomas, was a co-pilot on the doomed flight.

The brick memorial honoring McGuinness, Jay Hayes and James Trentini bears a plaque that reads: "Always Flying High. September 11, 2001. Never to be Forgotten."

The attacks loomed large in more traditional Memorial Day celebrations, and helped draw larger-than-usual crowds to services and parades.

"I am happy to see that so many people came out," said Army veteran Artie Clay at a service Sunday at Lee Street National Cemetery in Danville, Va. "You have to think that we may be seeing more of these headstones with our troops in Afghanistan."

Peter Shoars, a retired Green Beret who lives in Spotsylvania, Va., said he senses a national pride that wasn't evident when he was serving in Vietnam.

"It's completely different," he said. "In our country, we've had a lot of calm Memorial Day weekends where we never even looked back. We need to honor our deceased veterans, all veterans, and now all people."

In Timonium, Md., six names of people killed in the attack on the Pentagon were added to Children of Liberty Memorial, which was dedicated in 1990 to Maryland military personnel killed by terrorists.

The name of Staff Sgt. Walter "Trae" Cohee of Mardela Springs, Md., also was added. Cohee was killed on Jan. 20 when the helicopter he was riding in crashed outside Afghanistan's capital of Kabul.

"I knew my son was going to be something special, but I never dreamed that he would receive this much attention," said his mother, Jeanne Cohee. People from various branches of the military came up to hug her.

The Associated Press contributed to this report.