The World Trade Center had this fascinating opacity: two steel-grey slabs stopping thought. The more you looked at it, the less it gave you back. The Twin Towers came out of the minimalist aesthetic of the late 1960s,

Donald Judd sculptures: their only decorative adornments were those aluminum Y’s, provoking you by their tight-lipped abstraction, like the curved curlicues in a mosque screen, or like a series of why’s. Were they clones derived from the DNA of some Platonic ideal? Were they emblematic of containerization, which had destroyed the Port of New York: the container being that standard, infinitely replicable rectangle, everywhere the same height, length and depth? Shining like aluminum altars, 1,350 feet tall, the Twin Towers were our Stonehenge. Their architect, Minoru Yamasaki, was asked why he made two of them, side by side, instead of one gigantic structure, and he is said to have replied (the story may be apocryphal, but it’s a good one anyhow) that double the height would have destroyed human scale.

I never found them offensive or overbearing, neither did I love them; they didn’t invite dislike, they were too polite, eight-hundred pound gorillas in tuxes, having no need to beat their chests. (When they replaced the Empire State Building in the remake of King Kong, they offered the creature a too smooth, unvaried façade to convey precarious perching.) They were at once the most dominant and least assuming facet of the New York skyline: Don’t mind me, they said.

It took seven years and a billion dollars to build them. Putting together the deal required immense muscle, supplied by David Rockefeller at the Chase Manhattan Bank, his brother Nelson, then Governor of New York (who stocked one tower with state workers when the building failed to attract tenants), and the considerable resources of the Port Authority of New York-New Jersey. Austin Tobin, then head of the Port Authority, kept up the masquerade that the spanking new towers were somehow going to be given over to trade and port functions. “How did the Port Authority–chartered to safeguard the economic health of New York’s regional maritime commerce–become the agent, a half century later, of the port’s displacement and decline. And what caused America’s most venerable planning and development agency–once imbued with the high-minded public service doctrines of Woodrow Wilson–to transform itself into the world’s biggest real estate speculator?” demanded Eric Darton, in his book about the World Trade Center, “Divided We Stand.” While I don’t think the agency could have done much to keep the port in Manhattan, it does take gall to present to the public a real estate speculation as a consolidation of port services, at the very moment that these functions were being transferred to New Jersey. We were led to envision the twin towers as the vertical equivalent of all those shipping companies and counting-houses that once lined the docks, of all the shipbuilders, importers, commission merchants, marine insurance companies, brokers and lawyers whose Whitehall Street offices had overlooked the harbor.

Still, you have to hand it to them: the World Trade Center went from being a white elephant, when they began opening in 1972, to near-full occupancy of ten-million square feet of office space. Not only did it initiate the resurgence of Lower Manhattan, but its dug-out foundation stones were re-used as landfill to make Battery Park City, the true center of that revival. By 2001, the World Trade Center was valued at $1.2 billion, and the Port Authority had managed to lease the buildings for ninety-nine years to a consortium led by Larry A. Silverstein for $3.2 billion. The city and the agency were licking their chops, contemplating how they would spend the huge profits resulting from that privatization. The electronics shopkeepers of Radio Row whose district had originally stood in the World Trade Center’s path were long forgotten. But then, on September 11, 2001, the towers joined the palimpsest of multiple erasures, like a child’s magic slate, which is New York.

Now that they are gone, their absence reasserts how much they climaxed the southern tip of Manhattan. Their silvered profiles ashimmer against a blue sky, like matching cigarette cases, or at night, when they became moody and noirish, were poetic postcard effects achieved only at a distance; up close, they seemed blandly off-putting, and oppressive at street level, like most 65 mph architecture built in that era.

To the rest of the world–though, curiously, I would maintain, not to native New Yorkers, like myself, who would always regard the twin towers as parvenus, compared to the Empire State Building, the Chrysler or the Woolworth–the World Trade Center symbolized the Big Apple, and beyond that, the might of America, the Great Satan. Certainly the twins had the richest and most imaginative of meanings, a mystic temptation one can only speculate on, to the suicide terrorists of the Islamic jihad who attacked them not once but twice. The first time, in 1993, despite the tragic loss of life and damage to the buildings, the towers remained standing, seemingly impregnable. The structural design had called for each tower’s skin to be its main strength, through light glass-and-steel facing threaded by steel columns. These columns gave the buildings their stiffness, while a cluster of central columns and steel trusses helped hold up each concrete floor. “Redundancy,” the engineers call that structural backup that ensures a building’s resilience, even if damaged–a word that also fit the WTC aesthetically and, now, historically. The twin towers were very strong, nothing compromised in the way of construction, an engineering tour de force; but no building, as we discovered, is meant to take the brunt of a jetliner, gorged with jet fuel, shearing through its midsection. When they collapsed, they fell straight down, not forward. Like the good soldiers they were.