The psychology of the city has changed. It has changed most, of course, for the bereaved, the friends and family of those who died three years ago.
The most authoritative profile that has been made of them reveals continuing mental unease.
The research shows that nearly half say they still do not get a good night's sleep. About a fifth attend religious services more than they used to. And three-quarters of them are fearful of another attack.
Apart from this pervasive anxiety, the psychology of this great organism of a city has changed in other ways. It is grouchier again.
The other night I watched a biology professor from Columbia University, no less, square up to a lad in a bar who had voiced the wrong political line on President Bush.
The calm of 12 September, 2001 has broken and gone, for good.
And the flags from that strange time have vanished too.
The US flag was a symbol of solidarity after the attacks
Just after the attacks, I went out and bought a sweater with the stars and stripes emblazoned across the front. It was a political statement about democracy, a personal statement that a small group of people would not intimidate me.
Across the city, it was the same. There were flags on aerials and flags in front windows, everywhere.
The Star-Spangled Banner had become a symbol of unity for the first time since Vietnam when it was a pro-war banner.
All that has changed now. Many flags have been taken down; they are a partisan symbol again.
The geography of the city has also changed in subtle ways.
New buildings now tend to have more space around them, space to act as a barrier against a truck bomb, according to the architects, so there's a wide public plaza around the new station at the site of the World Trade Center.
Seven World Trade Center is being rebuilt on a huge concrete plinth.
Architects here have also been debating the role of glass.
The new design rising from Ground Zero will have acres of shimmering surfaces. The idea was to make it light as a symbol of hope.
But the glass will be laminated to stop it shattering in a blast. There will be curtains of mesh to prevent shards shooting in.
It is, then, the architecture of fear.
There is also - strange to say - a bizarre side to all this.
A week or so ago I was in South Carolina, the heart of Confederate country. There is still a statue of a Confederate soldier outside the state legislature, with the Confederate flag - that symbol of the old racist South - a flag which I saw a man salute.
This, then, is not - on the face of it - quaking, trembling America.
All the same, even here you feel the fear.
Tucked away in Columbia, South Carolina's state capital, there is a small Muslim community that is quiet and respectable and keeps its head down.
If you ask these people, though, they will tell you about the indignity of travel, about the searches and the suspicious looks.
I met a man called Azar Usman, a very funny American Muslim.
He is a tall, imposing man who wears the full regalia - the long black robe, the long black beard, the black cap.
He is, he concedes with a smile, the very stereotype of a 9/11 hijacker. Now, when he gets on planes these days, he says the faces around him drop.
And when the plane finally lands, he senses the relief among his fellow passengers.
One of them even told him how he nearly stabbed Azar when the be-robed Muslim got up to go to the toilet.
So there is fear on all sides in America today.
One event, though, made me really sad and fearful last week.
I learned of it on the internet as I sat in my flat in Manhattan, looking out on the space left by the Twin Towers.
An Iraqi, who had fled from torture under Saddam Hussein, was beaten to death in the street.
It happened, though, not in South Carolina but much nearer home.
It happened where I come from, in Swansea in south Wales.
There's no American monopoly on fear.
From Our Own Correspondent was broadcast on Saturday, 11 September, 2004 at 1130 BST on BBC Radio 4. Please check the programme schedules for World Service transmission times.