New York - Americans mark the 11th anniversary of the attacks on 11 September 2001 on Tuesday with relatively low key ceremonies that reflect a gradual dampening of passions around the emotional day.
The main ceremony will be the ritual reading at New York's Ground Zero of the names of the 2 983 people killed both on 9/11 and in the precursor to those attacks, the 1993 car bombing of the World Trade Centre.
Relatives of the dead will take turns to read the names against a backdrop of mournful music.
They will pause for moments of silence marking the moment when four aircraft hijacked by al-Qaeda turned into fireballs - two smashing into the Twin Towers, one into the Pentagon and one crashing into a Pennsylvania field.
Another two moments of silence will be observed at the times the two towers collapsed, accounting for the vast majority of 9/11's victims.
However, this year New York Mayor Michael Bloomberg and other politicians will not take the podium at Ground Zero, in contrast with last year's 10th anniversary, when President Barack Obama led a long list of VIP guests.
No suspension of campaign
Obama and his wife Michelle will observe the anniversary with a moment of silence outside the White House, then visit the Pentagon memorial.
Vice President Joe Biden, meanwhile, will travel to Shanksville, Pennsylvania, where United flight 93 crashed after passengers attacked the hijackers and thwarted a worse disaster had it continued to its target.
The White House said Obama had been briefed by "key national security principals on... preparedness and security posture" for the anniversary.
But in keeping with the lower key atmosphere this year, there will apparently be no official suspension of the bitter presidential campaign.
Former president Bill Clinton will be campaigning for Obama and speaking out against Republican Mitt Romney at an event in Miami.
The passage of time appears to have cooled public attention to 11 September, particularly after the huge media coverage of the 10th anniversary, which many saw as a suitable moment for allowing commemorations to peak.
The killing by American troops of al-Qaeda founder Osama bin Laden in May 2011 has helped draw a line under 9/11, as has the opening of the Ground Zero memorial, which opened for last year's ceremonies.
A skyscraper at One World Trade Centre is near completion and is again the tallest building in New York, as were the Twin Towers before they fell down.
This year sees the publishing on Tuesday of a book by a former US Navy Seal who was among the troops that shot dead bin Laden in his Pakistani hideout.
The book describes in gory detail how the special forces killed the fugitive, then radioed back the news, saying it was "for God and country".
The Pentagon has threatened legal action against the author who uses the penname Mark Owen, but has been outed by the US media as Matt Bissonnette.
Last week, Obama said in a radio address that the United States is "stronger, safer and more respected in the world" since 9/11.
But his Republican opponent has accused Obama of weak leadership during the Arab Spring turmoil and of failing to be tough enough on Iran's government.
In Afghanistan, which once hosted bin Laden, US troops continue to struggle to overcome the Taliban guerrilla army.
Most foreign troops are scheduled to withdraw by the end of 2014, handing over responsibility for combat to Western-backed Afghan government forces.