At nightfall, two huge columns of light resembling the twin towers were beamed skyward from a lot next to ground zero in a second memorial to the dead. The "Tribute in Light," made up of 88 high-powered searchlights, will be displayed nightly until April 13.
"I like the idea of the lights," said Caryn Wiley, who lost her father in the attacks. "It'll serve as a subtle reminder, and that's important, especially for people who didn't lose anyone."
In Washington, President Bush marked six months since Sept. 11 by urging nations with militants linked to al Qaeda to help "remove the terrorist parasites"
CBS News White House Correspondent John Roberts reports that Mr. Bush also set his sights on what he called the growing threat of terror on a catastrophic scale and on the efforts of rogue states like Iraq to acquire nuclear weapons.
"Men with no respect for life must never be allowed to control the ultimate instruments of death," Mr. Bush said.
The President also warned specifically that Yemen was in danger of becoming another Afghanistan.
"Every terrorist must be made to live as an international fugitive, with no place to settle or organize, no place to hide, no governments to hide behind and not even a safe place to sleep," Mr. Bush said.
Mr. Bush spoke on the White House South Lawn to mark six months since the Sept. 11 attacks. The event included about 1,300 people, including members of Congress, more than 100 ambassadors and about 300 family members who lost relatives in the attacks.
He said the United States was actively assisting the governments of the Philippines, Georgia and Yemen to quell militants linked to al Qaeda and said Yemen in particular was vulnerable. "In Yemen, we are working to avert the possibility of another Afghanistan," he said.
"At that hour we saw the worst of mankind," Gov. George Pataki said. "We saw the face of evil."
Former Mayor Rudolph Giuliani told the crowd it must look to the victims "for our inspiration and our sense of purpose. They would want us to lift up our heads very, very high."
Sept. 11, 2001 to March 11, 2002
Church bells rang across the city, and the names of the 23 police officers killed were read aloud at 8:30 a.m. at police precincts.
Capt. David Barrere recited the names as two dozen officers lined up on the sidewalk outside the 76th Precinct in Brooklyn. "They were called on to act and did so with the highest valor," he said.
The 343 firefighters killed in the trade center were honored separately with a bell-ringing at the morning service, where a message from President Bush was also read. Guests, including many victims' relatives, were given yellow daffodils.
Mr. Bush marked the six-month point during a ceremony at the White House, joined by more than 100 ambassadors as well as relatives of some victims and members of Congress.
"History will know that day not only as a day of tragedy, but as a day of decision when the civilized world was stirred to anger and to action," he said, calling on the world's nations to press the fight against terrorism.
At the Pentagon, where 189 peopled died on Sept. 11, Defense Secretary Donald H. Rumsfeld met with military leaders from the nations in the anti-terrorism coalition.
In Shanksville, Pa., church bells tolled at 10:06 a.m. in memory of the 44 victims of the crash of United Flight 93, the fourth hijacked jet that day. It went down in the countryside, apparently after some of the passengers fought back.
At Battery Park, city officials dedicated a sculpture damaged in the attack as a temporary memorial.
"The Sphere," a steel and bronze sculpture that stood in the trade center plaza, was gashed and partially crushed by falling debris. It was created in 1971 by artist Fritz Koenig and was dedicated as a monument to world peace through international trade.
"It survived the collapse of the twin towers, as did the idea that catalyzed its creation: a peaceful world based on trade and the free movement of people and ideas," Mayor Michael Bloomberg said. "This is just a temporary memorial. ... The real memorial will be in our hearts."
Among those paying tribute was Edwin Morales, who lost his cousin, firefighter Ruben Correa.
"I know some people say this is too hard, but this is something I need," Morales said. "I need to be here."
Across the city, at a Queens church, hundreds of firefighters attended the funeral of Richard D. Allen. The Fire Department has held 148 funerals in the six months since the attack.
The names of the victims from the trade center, the Pentagon and the plane crash in Pennsylvania were read aloud at St. Paul's Chapel in lower Manhattan. The church was a relief center during the months after the attack, and still serves breakfast to recovery workers digging through the rubble.
At ground zero, work stopped during the moments of silence. Among those looking on nearby were Harlan and Diane Kirschner of Los Angeles. They found solace in the expressions of sympathy from other visitors.
"For so much evil that hit, there's a lot of love around," Diane Kirschner said. "That's what I think of when I look."