Last Updated 11:34 a.m. ET
Moments of silence were observed in New York City Sunday on the tenth anniversary of the terror attacks that destroyed the World Trade Center and killed nearly 3,000 people.
"Ten years have passed since a perfect blue sky morning turned into the blackest of nights. Since then, we have lived in sunshine, and in shadow," said New York City Mayor Michael Bloomberg, just minutes after members of the Brooklyn Youth Choir performed the National Anthem.
"And although we can never 'unsee' what happened here ... we can also see that children who lost their parents have grown into young adults, grandchildren have been born, and good works and public service have taken root to honor those we loved and lost."
Sixty bagpipe players and drummers led the World Trade flag through the memorial, where the flag was unfolded and held aloft by the Honor Guard.
Noting that the words of writers and poets have been used to express what is in our hearts, Bloomberg recalled Shakespeare in saying, "Let us not measure our sorrow by their worth, for then it will have no end."
President Barack Obama stood before the white oak trees of the new Sept. 11 memorial and read Psalm 46 from the Bible, after a moment of silence at 8:46 a.m., when the first jetliner slammed into the World Trade Center's north tower a decade ago.
"God is our refuge and strength," the psalm said. "He dwells in his city, does marvelous things and says, be still and know that I am God."
President George W. Bush read the words of another president, Abraham Lincoln, whom he said "understood the cost of sacrifice, and reached out to console those in sorrow as best he could."
Reading a letter written to a mother who'd lost five sons in the Civil War, Mr. Bush said, "I pray that our Heavenly Father may assuage the anguish of your bereavement, and leave you only the cherished memory of the loved and lost, and the solemn pride that must be yours to have laid so costly a sacrifice upon the altar of freedom."
Also speaking were family members who lost loved ones on that day. Peter Negron, was 11 years old when his father, who worked on the 88th floor of the World Trade Center, died. Negron had read a poem at the 2003 commemoration about how wanting to break down and cry. "Since then I've stopped crying, but I've never stopped missing my dad. He was awesome," Negron said.
Negron recalled that he's tried to teach his younger brother all the things his father had taught him, like riding a bike. "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."
Negron said he wants to become a forensic scientist. "I hope that I can make my father proud of the young men my brother and I have become. "
Tales of heroism were told. Retired New York City Police Officer James Smith talked of Police Officer Moira Smith, who ran into the towers time and time again to save as many people as she could, before dying when the South Tower collapsed. "Moira sacrificed all that she had, and all the richness of life that laid before her in order to save just one more person."
"Today we choose to remember and share the joy Moira brought to us all and we vow that she will always live in our hearts," Smith said.
Also featured at today's ceremony were musical performances by the Brooklyn Youth Chorus; cellist Yo-Yo Ma, who played a Bach Cello Suite; James Taylor, who sung "Close Your Eyes"; flutist Emi Ferguson, who played "Amazing Grace"; and Paul Simon, who sang "Bridge Over Troubled Water."
Bells were struck to mark the hijacked airliners that struck the Twin Towers, fall of the World Trade Center, the attack on the Pentagon in Washington, D.C., and the crash of Flight 93 in Pennsylvania; and the names of the dead were read.
New York Governor Andrew Cuomo quoted President Franklin Delano Roosevelt who defined the four essential human freedoms on which the American Dream is based: Freedom of speech and expression; freedom to worship; freedom from want; and freedom from fear.
"Freedom means the supremacy of human rights everywhere," Cuomo said.
New Jersey Governor Chris Christie also turned to a poet, Mary Lee Hall, who wrote "Turn Again To Life":
"If I should die and leave you here a while,
be not like others sore undone,
who keep long vigil by the silent dust.
For my sake turn again to life and smile,
nerving thy heart and trembling hand
to do something to comfort other hearts than thine.
Complete these dear unfinished tasks of mine
and I perchance may therein comfort you."
"No words cried out so fully from the broken heart of our nation as those of a poem called "The Names," written a year after the attacks, by the United States' Poet Laureate, Billy Collins," said former New York Governor George Pataki. He read the last verse:
"Names etched on the head of a pin.
One name spanning a bridge, another undergoing a tunnel.
A blue name needled into the skin.
Names of citizens, workers, mothers and fathers,
The bright-eyed daughter, the quick son.
Alphabet of names in a green field.
Names in the small tracks of birds.
Names lifted from a hat
Or balanced on the tip of the tongue.
Names wheeled into the dim warehouse of memory.
So many names, there is barely room on the walls of the heart."
Former New York City Mayor Rudy Giuliani quoted Edna St. Vincent Millay:
"Gently they go, the beautiful, the tender, the kind;
Quietly they go, the intelligent, the witty, the brave.
I know. But I do not approve. And I am not resigned."
Earlier, Mr. Obama and Mr. Bush bowed their heads at the trade center site and ran their hands over the bronze-etched names of the victims of the attack.
The presidents were joined by their wives as they walked up to one of the two reflecting pools built over the towers' footprints, part of a Sept. 11 memorial that was to open later in the day for relatives of the victims.
The president and former president later embraced family members and talked to dignitaries, including Bloomberg, former Mayor Rudolph Giuliani and the governors of New York and New Jersey.