"Let us not forget as we gather here today that our nation is still at war," President Barack Obama said after laying a wreath at the Tomb of the Unknowns.
"When they give their lives, they are still being laid to rest in cemeteries in quiet corners across our country, including here in Arlington," he said. He told the stories of three soldiers who had died. Each had been devoted to their mission and were praised by others for saving lives.
Hours later, veterans from conflicts from World War II to Afghanistan and Iraq gathered in Atlanta to dedicate a new veterans' park. Soldiers, airmen, Marines and seamen looked on as veterans and military family members sprinkled soil, sand and water from battlefields and waterways across the world.
Retired Army Lt. Col. Rick Lester called it "a reminder of our country's timeline of freedom." A 26-year veteran with multiple tours in Vietnam, Germany and Korea, Lester conceived the ceremony as a way to honor living veterans and those who never made it home.
The pilot recalled in detail the numbers of men lost on missions he flew in Vietnam. "All I can think about is how those were some of the greatest guys I ever met and what they would have done for this country once they got back," he said.
The soil and sand ranged from Revolutionary battlefields like Lexington and Concord to Tikrit in Iraq. There was none from the Civil War, Lester said, because "that was a time that our country was divided."
Battlefield remnants were mixed in a helmet Lester's father wore on D-Day in France in 1944. They were sprinkled from cups that his uncle, a Marine, used in World War II. His father lived. His uncle was killed in action.
Susan Jimison poured water collected from the Hudson River, Chesapeake Bay, Atlantic Ocean and Pacific Ocean.
Her brother, Mark Clotfelter, was a helicopter pilot shot down June 16, 1969, in Vietnam. The 22-year-old was later confirmed dead. Jimison was 14 at the time and recalled how a politically unpopular war affected the way her brother's death was treated. "Nobody talked about it," she said.
It wasn't until many years later that she started trying to learn about his military service and those who served alongside him. Now, she's married to a man, Michael Jimison, who flew with him, and she's writing a book about their company.
It's important, she said, for Americans to learn the personal stories behind military history and international conflict. "My brother died doing what he loved doing," she said.
New York Mayor Michael Bloomberg joined military leaders and others at the Soldiers' and Sailors' Monument in Manhattan. He later encouraged New Yorkers to celebrate the day and the good weather but also "remember the sacrifice that was made so that we could be here."
At the National World War II Museum in New Orleans, about 20 bicyclists clustered around veteran and museum volunteer Tom Blakey. The paratrooper in the 82nd Airborne Division jumped at Normandy on D-Day - June 6, 1944 - and in May 1945 helped liberate the work camp at Wobbelin in northwest Germany.
"Most of us wondered why we were there, killing people and being killed," he said. "We didn't do anything to deserve it. When we got to that camp and saw what was there, the lights came on."
The cycling group makes regular weekend training runs, and on Monday started a Memorial Day ride about seven miles away at the national cemetery in Chalmette, where the Battle of New Orleans - the last in the War of 1812 - was fought.
In South Sioux City, Neb., a statue honoring a Navy dog handler was unveiled in his hometown. The statue of Petty Officer 1st Class John Douangdara (dwung-DEHR'-ah) and his dog, Bart, is part of a five-acre dog park that's named for Douangdara. Douangdara died along with 29 other Americans in August 2011 when a military helicopter was shot down in Afghanistan.
Across much of New England, several days of heavy rain gave way to sunny skies for parades in towns large and small.
In Portland, Maine, kids and even pets displayed the Stars and Stripes as veterans, youth groups law enforcement officials and civic organizations paraded to Monument Square to the tunes of a marching band, sirens from a police car and the rumble of motorcycles.
For some veterans, it was a somber event.
Richard Traiser, a Marine injured when his tank came under attack in Vietnam, helped deliver a three-volley salute with the Marine Corps League.
Memorial Day gives those who served an opportunity to get together and remember friends who didn't make it.
"I think about them a lot, especially the people I lost in my platoon," Traiser said. "I don't dwell on it in a morbid way, but it's on your mind."
In Connecticut, a Waterford man who was killed in the Vietnam War was honored with a hometown park area named for him. Arnold E. Holm Jr., nicknamed "Dusty," was killed when his helicopter was shot down on June 11, 1972.
The holiday weekend also marked the traditional start of the U.S. vacation season. AAA, one of the nation's largest leisure travel agencies, expected 31.2 million Americans to hit the road over the weekend, virtually the same number as last year. Gas prices were about the same as last year, up 1 cent to a national average of $3.65 a gallon Friday.
At the American Airpower Museum on Long Island, N.Y., a program honored Women Air Service Pilots, or WASPs, who tested and ferried completed aircraft from factories to bases during World War II. Thirty-eight died during the war, including Alice Lovejoy of Scarsdale, N.Y., who was killed on Sept. 13, 1944, in a midair collision over Texas.
"It's very important that we recognize not only their contribution to American history, but women's history," said Julia Lauria-Blum, curator of the WASP exhibit at the museum. "These women really blazed a path; they were pioneers for women's aviation. And most important, they gave their lives serving their country and must be honored like anyone else on Memorial Day."
Associated Press writers David Sharp in Portland, Maine; Janet McConnaughey in New Orleans; and Darlene Superville in Washington contributed to this report.