I t was always fashionable to deride the twin towers of the World Trade Center. Too bland. Too sterile. Too glitzy. They cost too much, and they took forever to rent out.

Now, of course, we’d give anything to see them again.

Minoru Yamasaki’s buildings, designed in collaboration with Emery Roth, usually inspired mixed feelings. They did look a little barren in the middle of that vast plaza. The tracery of the exteriors was almost universally misunderstood as applied decoration, badly underscaled at that. But there was nothing like them as a symbol of New York, of America, of power and freedom. They stood over New York Harbor looking for all the world like the gateway to the United States, and having the Statue of Liberty standing in front of them didn’t hurt the symbolism one bit.

Designed beginning in 1965, and completed in 1973, the 110-story towers never really got their due. Briefly the tallest buildings in the world, they were quickly surpassed by others. They were actually engineering and architectural marvels, and the proof of their greatness came in their last hour.

Yamasaki’s commission was first presented to him as a very tight package of parameters: The Port Authority of New York wanted twelve million square feet of floor space, and new tunnel and subway facilities- all on a sixteen-acre landfill site. The budget was not particularly lavish for what was envisioned- $800 million. Yamasaki met the challenge, with elàn to spare.

His first concern was to create something that gave an impression of distinction. He had long felt that the beauty of the Empire State Building was difficult to appreciate, owing to a complete lack of any approach that would allow onlookers to grasp the scale of the design. The plaza was the answer to that problem, but leaving so much open space meant that the buildings on it would have to be very tall to answer the stated needs for square footage. The twin-tower concept came after careful consideration of other options: One main building was too massive, and several small ones too much like “a housing project”, in Yamasaki’s words. The idea of two twinned major buildings had exactly the right touch of distinctiveness; the key to the project had been found.

The two buildings were designed to contain nine million square feet of floor space; other, smaller buildings on the site would contain the other footage. Yamasaki’s design quickly shaped up as an engineering wonder. The towers contained a central core enclosing elevators and utilities; the core also carried the weight of the building. For sixty feet in every direction from the core, floor space was designed without columns of any kind; the prefabricated steel floor structure was only 33 inches deep. The last structural contribution was made by an unconventional outer wall system of very slender steel columns spaced only 39 inches apart, forming an exoskeleton. Connected to the prefabricated floors, the myriad of exterior columns helped to hold the rest of the structure in tension. The result was amazingly light and strong, with the stiffness necessary to withstand wind loads.

Yamasaki also maximized rentable square footage with his “Skylobby” concept. One of the problems in building a very tall building is that people have to be moved up and down by elevator. The bigger the building, the more elevators needed, and the more square footage consumed by their shafts. Yamasaki made the tower’s elevator system much less space intensive by creating a system of “local” and “express” elevators; one rode express to a Skylobby, then changed to a local elevator to get to the desired floor.

The buildings opened to mixed reviews. They were seen as an engineering accomplishment, but the exterior detailing left something to be desired in the eyes of some onlookers. The columns forming the exoskeleton were expressed as a delicate tracery on the outer surface; people who thought they were looking at conventionally-constructed skyscrapers tended to dismiss the tracery as applied decoration.

The towers also took a while to fill with tenants. The middle 1970’s were recession years, and the World Trade Center was top-of-the-line luxury space. They did fill eventually, and the Port Authority worked hard to enhance their image. The plaza was used as the Emerald City for the 1978 movie version of “The Wiz”, and Ford premiered its new Lincoln Versailles automobile by having one hoisted up all 110 floors to the Windows On The World restaurant for a press shindig.

The years went by for the buildings fairly uneventfully until 1993, when they began to play a role never imagined by Yamasaki or the Port Authority. The potent symbolism of the glittering twin towers was well understood by terrorists, who saw the possibility of their damage or destruction as the most terrifying message they could send to America. The first attack came in 1993, with a truck bomb planted in the basement parking area of one tower, near columns the terrorists hoped would shatter, toppling the building. They miscalculated, and the building stood, but there were five deaths, numerous injuries, and damage requiring $300 million in repairs and retrofitting. Safety measures were increased, and evacuation procedures improved.

As the world knows, terrorists were not through with the buildings. On September 11, 2001, a hijacked airliner was flown by a terrorist into one of the towers, causing massive damage, and bursting into a 2000- degree fireball. Eighteen minutes later, a second hijacked plane hit the other tower, with identical results. Within the hour, both towers collapsed, with massive loss of human life.

The possibility of airliner damage to the towers had been provided for, to an extent. Because of the height of the buildings, each was designed to withstand the impact of a Boeing 707, the largest plane aloft in the late 1960’s. The Empire State Building had been accidentally hit by an airliner in the 1940’s, with minimal damage to the structure. In that simpler time, accidental impact was the only reason anyone could imagine for such an occurrence. No one foresaw terrorists deliberately flying planes at full tilt into occupied skyscrapers, and if they had, there was and is no way to design a building to withstand that.

Although the collapse of the towers was unexpected and swift, there were attributes of the buildings that may have made the situation somewhat better than it might have been. For one thing, the tension of those exoskeletal outer walls seems to have helped them hold together longer than conventional buildings might have, with their exterior columns 10 to 15 feet apart. The terrorist-guided airliners hit one tower on a corner- and in most buildings, there is no easier way to induce instant structural failure than to remove a corner column. Possibly because of their unconventional construction, the Trade Center towers were able to hold together the precious hour or so that helped many people escape with their lives. The collapse was due more to the fireball’s melting of steel beams in upper floors than to the impact itself; once the beams melted, the upper third of each building banged down onto the rest, dooming the towers.

For now, where there was once symmetry and symbolism, there is rubble, and smoke, and stench. There is unmitigated horror, and there is simple exhaustion. But this is America, and so there is already talk of rebuilding. New York Mayor Rudolph Giuliani has promised, “the skyline will be made whole again.” And one day it will be, after the dead are recovered, and mourned, and the site cleared, and the most difficult job of all is done.

We have to make it safe for new buildings to be there. And that, too, we will accomplish.