The United States marked the 10th anniversary of the terrorist attack on New York, Washington, and Shanksville, Pa. Sunday with memorial services at the World Trade Center (WTC), the Pentagon, and at a field in Pennsylvania -- all three of which are hallowed ground.

The New York services, at which 2,732 people were murdered, took place next to the tower that will be the initial one completed at the WTC site -- One World Trade Center -- which was draped in red, white, and blue lights Saturday nights. The annual Tribute in Light, -- two blue beams of light that extend to the clouds, and beyond.

President Barack Obama was joined by former Presidents George W. Bush and Bill Clinton, New York City Mayor Michael Bloomberg, former New York City Mayor Rudolph Giuliani, New York Gov. Andrew Cuomo and New Jersey Gov. Chris Christie.

Obama Read Psalm 46

President Obama read Psalm 46, which talks about God as our refuge and strength, a very present help in trouble, and Gov. Andrew M. Cuomo of New York read from President Franklin D. Roosevelt's 1941 State of the Union address, the famous four freedoms speech - freedom of speech, freedom of religion, freedom from want and freedom from fear anywhere in the world The New York Times reported Sunday.

Thousands gathered on a clear, warm Sunday morning to grieve where the twin towers of the World Trade Center once stood, Reuters reported. With security high and no traffic, there was an eerie silence where a decade ago the 110-storey skyscrapers collapsed after being hit by hijacked airliners, sending a cloud over lower Manhattan.

The somber ceremony -- with bagpipes, youthful voices singing the national anthem and firefighters holding aloft a tattered American flag retrieved from Ground Zero -- drew tears. Family members wore T-shirts with the faces of the dead, carried photos, flowers and flags in an outpouring of emotion.

For the first time, relatives saw the just-finished memorial and touched the etched names of their dead loved ones. Some left flowers, others small teddy bears. Some used pencils to scratch the names on paper, others took a photograph.

Bush Quoted Lincoln

Bush quoted former President Abraham Lincoln's letter in 1864 to a Union mother whose five sons died in the Civil War, the United States' greatest internal crisis.

President Lincoln not only understood the heartbreak of his country, he also understood the cost to sacrifice and reached out to console those in sorrow, Bush said.

Many relative and other mourners cried as the names of the dead were read, by wives and husbands, fathers, mothers, sisters, brothers and children, some choked with emotion at their personal loss.

I haven't stopped missing my Dad. He was awesome, Peter Negron, who was just a child when his father, Pete, was killed in one of the stricken towers, told Reuters. I wish my Dad had been there to teach me how to drive, ask a girl out on a date and see me graduate from high school and a hundred other things I can't even begin to name.

The September 11 National Memorial, officially the National September 11 Memorial and Museum at the World Trade Center, includes two plazas in the shape of the footprints of the Twin Towers with cascading 30 foot waterfalls. Around the perimeters of pools in the center of each plaza are the names of the victims of the September 11 attacks and an earlier 1993 attack at the trade center.

At the Pentagon Sunday morning, 1,600 people, including 100 survivors, gathered at the site of the attack on the nation's military headquarters. Under heavy security, service members lay wreaths on each individual bench at the 9/11 memorial, beneath the backdrop of a huge American flag hanging on the spot the airplane struck, The Washigton Post reported Sunday.

Vice President Biden paid tribute to the 9/11 generation of 2.8 million service members who signed up to fight wars in Afghanistan and Iraq, and be deployed in other dangerous regions, in the wake of the terror attacks.

Later in the morning Obama traveled to Shanksville, Pa. to pay his respects at the Pennsylvania site where a hijacked jet crashed during the Sept. 11 terrorist attacks.

Obama and his wife, First Lady Michelle Obama, visited the Wall of Names. Each of the 40 marble slabs is inscribed with the name of someone killed in the crash of United Flight 93, The Associated Press reported Sunday.

The hijacked plane slammed into a field in Shanksville, 60 miles southeast of Pittsburgh, as the passengers and crew tried to regain control of the aircraft from the four hijackers.

Investigators later determined that the hijackers intended to fly the plane into the White House or the U.S. Capitol, where Congress was in session on Sept. 11, 2001.