Seven major projects -- each with its own team -- are part of the $18 billion redevelopment of the former World Trade Center. They have needed to cooperate with one another because they share space in a four-level basement at the site. The plan is to have the memorial plaza ready for the 10th anniversary of the Sept. 11, 2001, attacks. One reason that might happen? "Three engineers from the Port Authority -- Mark Pagliettini, Tom O'Connor, and Dave Puza -- were working on this," says Christopher Ward, executive director of the Port Authority of New York and New Jersey. "Then Pagliettini said, 'Maybe we can just build it from the top down.' These three great engineers made it happen."