Considering he is both an architect and a structural engineer, it is not surprising that Santiago Calatrava considers the professions inextricably intertwined. "There is a symbiosis between architecture and engineering," says Calatrava. "Looking at architects and engineers as separate disciplines is a convention and a new thing," says the designer for the $2.2-billion World Trade Center Transportation Hub in lower Manhattan.

Calatrava considers the separation unnaturala consequence of the evolution of the profession, related to the recent development of specialty consultants. With that outlook, it is also not surprising that the architecture is the structure and vice versa in most of Calatrava's buildings. The two public halls of the WTC hubthe icon reminiscent of a dove and another space, just below grade, with undulating concrete archesare no exceptions.

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Natural light is another significant "material" for Calatrava. Flooding a space with daylight, or offering a view of the sky, helps add a dimension beyond pure functionality, says the A-E. This is important, for the WTC hub will be part of the "heritage for the next generation, full of emotion and the grandeur of the moment," explains Calatrava.

Three years ago, after landing the WTC hub commission, Calatrava moved to New York City from Zurich. But long before Sept. 11, 2001, he had dreamed about working for the Port Authority of New York and New Jerseyhis client for the hub. Also a bridge designer, Calatrava admires the George Washington, the Bronx-Whitestone, the Throgs Neck and the Verrazano-Narrows bridges, designed for the PA by Othmar Ammann. Long a hero of Calatrava's, Ammann was educated at the Federal Institute of Technology in Zurich, where Calatrava earned a doctorate in civil engineering.

See one Calatrava building and the rest are easily identifiable. "I have found that every project you build poses problems that can be solved only by the next project," he says. "This is why my designs often develop as a series."

The WTC hub carries forward ideas Calatrava explored in earlier projects, such as the Lyon Airport Station in France or Stadelhofen Station in Zurich. "I feel it is very fortunate that I had these earlier ideas to draw on, because the function of the transportation hub is so complex, the site is so dense and the need for symbolic expression is so great, that I have had to call on every bit of my experience," he says. Though his ideas may come from earlier projects, Calatrava says the hub project is not comparable to any other because of its intense symbolism.