GROUND Zero, the vast site that once housed the World Trade Centre, is the clearest symbol of the loss suffered on September 11.

Once a towering monument to American capitalism, now all that remains is a seven-storey crater.

The smoke, dust, tangled wreckage and rubble that followed the collapse of the Twin Towers have gone, and fires that smouldered deep underground for months after the atrocity are out.

But Lower Manhattan has undergone some other dramatic and unexpected changes. More than three million visitors are expected to view the crater this year, compared with the 1.8 million people who used to go up to the World Trade Centre's observation deck each year.

Critics have dubbed the area 9/11 World after the arrival of guides charging £10 to show key points on the site and countless street traders selling Twin Tower prints, books and American flags.

A round-the-clock recovery operation moved 1.62 million tons of debris from the 16-acre site to a landfill in Staten Island and in May, months ahead of schedule, a special ceremony was held to mark the clean-up when an empty stretcher draped in the US flag was carried out to symbolise the bodies that were never found.

Engineers from Darlington-based Cleveland Bridge flew out to the site a week after September 11 to repair a 25-metre wall, which was used to protect the building from underground flooding. After the attacks, the rock anchors that stabilised the structure were damaged, leaving the wall leaning against the rubble.

"We were there from the beginning and, at that stage, everyone was just stunned by what had happened. It was dreadful, horrific," said the company's technical director Jim Hughes.

"It was a potentially difficult and dangerous job but we came up with a very novel method of drilling out the existing anchors and putting in new ones.

"Everyone was working overtime to get the site cleared and it was pretty savage. We were working 24-hours a day, seven days a week until March this year, when we finally finished."

Now the clean-up is complete, no decision has been reached about what to build on the site of Ground Zero.

Six blueprints were recently put forward by the Port Authority of New York and New Jersey, a two-state agency which owns the land. They all included a cluster of buildings around open space and a memorial, but were rejected as "uninspired".

The central problem, which may never be resolved, is that Ground Zero has two roles to fulfil, the requirements of which pull designers in opposite directions.

The area is prime real estate in a city which desperately needs to get business moving downtown again; it is also the graveyard of more than a thousand victims of a brutal terror attack, whose remains were never found.

Former Mayor Rudolph Giuliani has called for a "grand, soaring memorial" while his successor, Mike Bloomberg, wants something simple that will be agreeable to businesses considering moving into the area.

New York State Governor George Pataki said the footprints of the towers should never be built on, a view shared by the vast majority of the victims' families, but the Port Authority wants the new development to replace the 11 million sq ft of office space lost in the World Trade Centre, leaving little room on the site to spare. The conflicting demands have left the plans in disarray.