Reflecting Absence Michael Arad, New York, NY

Mr. Libeskind says his design is filled with symbolism.

" Indeed, not just some buildings standing around but those buildings that embrace the memorial, spiral upwards just like the torch of the Statue of Liberty to the high point which is 1,776 feet [541 meters] high, a very symbolic and important date of the Declaration of Independence, and stand in homage to both 9/11 the heroes who perished there but also to the future of New York as a capital in many ways of the world," Mr. Libeskind says.

After Mr. Libeskind's design was chosen, Mr. Childs was named head architect of Mr. Libeskind's Freedom Tower. The modified skyscraper with more than 60 floors and a towering spire reaches 541 meters high, making it the tallest building in the world.

Now, more architects are involved in a web of projects from transportation hubs to cultural centers, and the details keep changing. Mr. Libeskind says the adjustments are mostly minor and inevitable, and his overall vision has prevailed.

"To anyone's eye, comparing the two schemes - the scheme in the competition and the scheme that is being built - I think only certain small details have been changed, and of course that is natural because the competition was not about designing every building and every window and every doorway," Mr. Libeskind says. "You can't do that for 10 million square feet of density, for public spaces of the memorial which will have five million people visiting them a year."

A memorial design was decided on last year, to honor the close to 3,000 people who lost their lives in New York City on September 11th. It includes a memorial wall that will list the names of the dead in random order.

That has angered some families of 9/11 victims. New York City Fire Department Lieutenant Jimmy McCaffrey lost his brother-in-law, Fire Chief Orio Palmer. Tape recordings revealed that Chief Palmer had climbed to the 78th floor of the south tower before it collapsed. His body was never found. Mr. McCaffrey says the ultimate recognition of sacrifice should come from respecting the dead, especially those who were never recovered, by not building on the footprints of the towers.

"To have it overshadowed just because of economic and political machinations is just wrong," Mr. McCaffrey says. "Many people feel that's where their loved ones died, that's their grave, that's where they're going to be buried, they're not going to have another place to bury somebody because they haven't found any remains, they haven't identified any remains of more than half the victims of that day. That in essence is their grave. And you wouldn't do that in a graveyard. You wouldn't do that on anyone's grave, build something or trample on it, if you will."

Mr. McCaffrey is now the co-chair of Advocates for 9/11 Fallen Heroes, a group that is lobbying for the victims of the terror attack to be identified more fully on the memorial wall. His group wants the rescue workers to be identified by firehouse company number or police precinct, and the civilians to be identified by their place of work, such as Cantor Fitzgerald, a firm that lost close to 600 employees. That way, Mr. McCaffrey says, he hopes future generations will not forget the people who perished in the terror attacks.