After intense competition and debate, a design by the architect Daniel Libeskind was finally chosen for the Ground Zero site, where the World Trade Center complex once stood.
The 26-hectare plot has carried enormous symbolic weight since the terrorist attacks of September 11, 2001 destroyed the great towers that once stood there. It has been, by turns, a place of grief, loss and anger; it is now also a place where hope for healing is concentrated.
Daniel Libeskind's design, which includes plans for a dramatic sunken memorial as well as a soaring crystal-like spire, has received high marks for sensitivity to all these concerns. But there are awesome engineering challenges that Mr. Libeskind will also have to address in rebuilding Ground Zero.
The World Trade Center towers were utterly destroyed when they collapsed on September 11. But the "slurry" or retaining wall that served as part of the foundation to the original complex held firm.
Architect Daniel Libeskind sees this wall as a symbol for democracy itself. His design for a memorial keeps a major part of this concrete wall intact and exposed, giving it an almost raw appearance.
"Well, that's true. But there is something very inspiring about seeing the real wall. They not only withstood the attack, but they are also something that speaks' right from the bedrock of New York to its future in the skies," he said. "It is something that is so moving, and also, [it is] a kind of miracle of construction. Because not only were the towers a miracle of height, but the foundations which support the entire edifice and continue to support it is really a miracle of construction. So I really wanted the public, the citizens to be aware of where they are standing. It really is a sacred ground. It is a spiritual space."
The exposed slurry walls of the memorial will rise only about 10 meters. That is less than half the original 22-meter height which Mr. Libeskind had planned for in his first Ground Zero design. Paul Goldberger, architecture critic for The New Yorker magazine, explains the engineering rationale at work here.
"It turns out that his original expectation that you could just leave the wall turned out to be wrong," said Mr. Goldberger. "The wall, that concrete wall that is 70 or so feet high, that supported the foundation of the World Trade Center and kept the water out, since it's really landfill right near the Hudson River, needed the horizontal support of floors pushing… against it to balance it out. And when you don't have that, eventually the wall would crack and the pressure from the river on the other side would break through. So it needs bracing and support."
Mr. Goldberger says that, over time, a plan evolved that would place a huge horizontal partition against the slurry wall, somewhat like an artificial floor. This will serve as buttress support.
"… And then the memorial ground in effect would begin halfway up at about 30 feet below grade level, and that would be become a lawn," he said. "So it would be a little bit like a sunken park with that wall exposed. That's an engineering issue that has to do with the technicalities of engineering. It doesn't really have that much to do with the terrorist threat."
The collapse of the twin towers destroyed most of the transportation infrastructure underneath the complex - including subway and regional train lines. The new Ground Zero plan includes a major new transportation center, a resource Mr. Goldberger says New York badly needed anyway.
"The idea of a great transit center is to pull together a lot of these subway lines that have been sort of a confused spaghetti mix of disorganized things over the years and use this tragedy as an opportunity to make that all better and much more organized and pull them together into something that would be a great vestibule, a kind of front door to Lower Manhattan," said Mr. Goldberger. 'Using this tragic event as an opportunity to make the city better: I think that is one of the great responses to terrorism that we can imagine."
September 11 was not the first time the World Trade Center complex had been a target of violence. Many New Yorkers recall the day in February 1993, when Middle Eastern terrorists set off a bomb in the tower's underground garage, killing six people and wounding over 1,000. Mr. Libeskind has been especially careful to design a complex that would be less vulnerable.
"We worked very strongly with security experts," he said. "The planning already of the Port Authority for the site has taken into account car parking, truck access, all the things we know now from the evils of the world we have to be careful about. Therefore the site has been thought about in terms of all those issues."
One reason so many people died on September 11 was the sheer height of the towers, which made escape difficult, almost impossible, for those on the higher floors.
Even though the spire at the top of the main office building in the winning design would make it the tallest manmade structure in the world if it were built today, the office-building portion of the structure would rise only to about 70 stories. Mr. Libeskind says that this limit makes both psychological and engineering sense.
"… And that is also the investors' thinking," he said. "I don't think there is any investor that will build today any building over 70 stories on that site. Because once you get past 70 stories we are into [a] whole new technology of escape.
"And I intend to use conventional means, which are well tested by fire brigades, by police units," he continued. "It doesn't demand sky lobbies, it can be evacuated safely and quickly and doesn't pose psychological or indeed terror threats. Very much these issue were upper[most] in my mind in designing not only the [overall] urban structure but also in designing each individual building."
Work has already begun beneath the Ground Zero site. Whatever form the complex ultimately takes, no one knows better than architect Daniel Libeskind that it will take persistence and know- not just big dreams, to get the job done.