From the opening bell, it was a day that rang with defiance

Two traders, Elliott Ronan and Louis Bisignano, emerge from a back door of the New York Stock Exchange into the narrow alley of New Street and make for their usual deli for "coffee and a little cry". They know they must gather themselves. The opening bell on this extraordinary day will be ringing in an hour.

Actually, their mood is one not so much of grieving ­ each man personally knew several of those still missing after last Tuesday's tragedy ­ but defiance. At 9.30am, the exchange is to reopen after its longest closure since the Depression. And they will have a part in America's answer to the terrorists: your crime shook us to the core, but today, less than seven days later, we are up and running again.

"You see what they did to us? It's like what happened to your country in the Forties," Mr Bisignano said. A trader for Brean Murray, he is wearing a red, white and blue ribbon, pinned to the bright green jacket he wears on the trading floor. "Well, we're going to show those bastards that we're still here and we're still standing and we are not going to be f***ing intimidated. And you can print that."

Nobody in the financial district early yesterday, where the smoke and dust still hung in the air from the twisted wreckage of the twin towers, lying just 300 yards away from the Stock Exchange on Wall Street, is in any doubt about what they are doing there. They are not just going back to work. They are joining in a symbolic gesture of America picking itself up and demonstrating its resilience.

And it is a gesture that is composed of many tiny miracles. Even at the weekend, this was a no-go zone for anyone but the search-and-rescue personnel themselves and soldiers of the National Guard in camouflage. The only others allowed in were the hundreds of technicians deployed to get the severely damaged infrastructure of the Stock Exchange working again. The streets around its building yesterday hummed with emergency generators and were a tangle of newly laid power and telephone cables.

Officials compared the impact of the towers falling to that of a very localised, but very serious, earthquake. Hence the need to restore communications. But many of the big investment firms, including American Express, Morgan Stanley and Merrill Lynch, had to overcome huge challenges to be ready for operations yesterday, moving thousands of employees to contingency locations, in many cases in available office space in New Jersey. Lehman Brothers moved 5,000 employees across the river. One company, Bear Stearns, even gave some of its spare offices to employees from rival companies.

And there are small miracles also of human courage on Wall Street. These people ­ about 180,000 souls work in the immediate vicinity of Wall Street ­ are the survivors of the Trade Centre attack. They saw it at close quarters. They ran across the Brooklyn bridge when the towers came down, many of them leaving behind friends they will never see again. This was their first time back to the scene of that waking nightmare.

It has taken Violet Avery, a broker at the Wall Street headquarters of the Bank of New York, more than two hours to get here from her home in Brooklyn. Several times, she was tempted to turn back, such was her fear. Now, at 9am, she is less than a block from her office, but can't bring herself finally to go through the door. Dressed in a smart brown business suit, she wears dark glasses to conceal the moisture in her eyes and holds a mask to her face.

"This morning, before leaving, I called my minister and asked him to pray for all of us coming back to Wall Street," Ms Avery confides. "I knew that we had to come, just to show them and to up the American economy again. But it's going to be very hard."

Sharon Weekes, 31, who travelled from her home in the Ozone Park section of Queens to return to work in the markets surveillance department of the NYSE, says: "I was crying in the shower this morning. I knew I had to come back, just to show up, but I was scared.I kept thinking that more of them were out there, waiting to strike us again."

Ms Weekes was dismissed soon after she arrived, told that only those people essential to the running of the trading floor needed to stay.

So she left with a colleague to walk two blocks north to Nassau Street and Liberty. There she took a camera from her leather handbag and took a snapshot of the view to the west.

It should be an impressive picture ­ right there, amidst the smoke, stands the remains of what was the outer casing of the south tower. About five storeys high, it is a jagged memorial to the perished.

For people such as Avery and Violet, help is on hand, if wanted. Ellen LeCroix is one of several professional counsellors positioned by the Red Cross around Wall Street, to help anyone in need. "I am trying to look in their faces to see if they are having a hard time," explains Ms LeCroix, standing just across from the Stock Exchange under the steps up to Federal Hall. As she speaks, she spots two women hugging one another near by in clear distress. "They both lost someone last Tuesday," she explains later.

Even the debris ­ the awful grey ash of pulverised concrete and glass ­ has been mostly swept away. The grass in the cemetery behind Trinity Church, the oldest in the city, which for days was under a blanket of singed documents and other papers that had wafted down from the towers before they collapsed, is green and pristine again and the tombstones are dusted clean.

There is a wartime feel on Wall Street that would have been bizarre only a week ago. Workers in suits and tassled shoes must show passes at checkpoints to soldiers with semi-automatic weapons. Most surreal, however, is the music. Fairground tunes and De Sousa marches that evoke Monty Python are coming from loudspeakers on the outside of the fortress-style building north of Wall Street that is the Federal Reserve. There is even a perky rendition of "God Bless America" on the xylophone.

By 9.30am, it is mostly just curiosity-seekers in the streets and journalists. The traders and brokers, as well as the myriad other employees in connected businesses, are now in their places of work.

Inside the Stock Exchange the mood is sombre. Richard Grasso, its chairman, calls for two minutes of silence. It is followed by another singing of "God Bless America" from an NYSE choir. Then, at last, at 9.33am, representatives of New York's heroes ­ its police and firemen ­ ring the bell and the trading begins.

The numbers start to plummet, but that was inevitable. For Louis and Elliott and for Violet and Sharon, what matters is that they are there. The systems are working. The terrorists can go to Hell.