Even on a brilliantly clear California day that hints at the coming spring, there is a sort of pall that hangs over the intersection of Washington and Montgomery Streets here.
The streets are busy, and most people don't even take note, yet the bulky white barriers that surround the soaring spike of the Transamerica Pyramid are an unwelcome reminder: that this skyscraper - like dozens of others across the United States - remains a potential terrorist target.
In the thousands of ways that Sept. 11 has refracted through American culture, the collapse of the World Trade Towers has also almost certainly ended America's obsession with building ever taller. Already squeezed by changing economics and shifting corporate values, this most obvious urban icon of wealth and power, the super tall skyscraper nearing 1,000 feet, is - for the moment, at least - a part of the past.
"It's pretty clear that in America especially, plans to build super-tall buildings - iconic buildings - will be on hold for a long time," says Jeffrey Heller, an architect at Heller Manus in San Francisco.
There are early suggestions of a shift in attitudes. In Chicago, plans for the new Trump Tower have been nearly halved since Sept. 11. What was tentatively planned to be, at 120 stories, the world's tallest building, is now set to go forward at 78 stories, making it the fourth-tallest building in the city.
In New York, one of the plans for the World Trade Center site has four 50-story buildings, rather than the two 110-story buildings that stood there previously. And as of last month, nearly 15 percent of the Empire State Building was vacant, even as leases slipped form $40 to $25 a square foot.
The concerns are not all about fear. Two officials investigating the World Trade Center disaster last week implored Congress to set new standards for construction of federal buildings - a proposal that could reverberate into private businesses, making it more costly to build taller.
Moreover, insurance for tall buildings is soaring. Metal detectors and bag searches are now de rigeur in the foyers of many of America's tallest buildings, and strictly kept guest lists determine who can and can't come in. It's far from an ideal business environment, some say.
"Who needs it?" says Martin Wolf, an architect in Chicago. "There are only so many fire drills that a company wants to go through."
Yet, in many ways, Sept. 11 was just the last blow for an icon already in decline. Since the days of the Great Gatsby and swing dancing, each economic boom has led to a new spate of mega-skyscraper construction.
The Roaring '20s gave rise to the twin spires of the Chrysler and Empire State Buildings. The 1950s and '60s culminated in massive projects like the Sears Tower and the World Trade Center.
The Reagan years sowed the seeds for urban monoliths from Atlanta to Los Angeles.
But during the last decade, something changed. The architectural offspring of the 1990s, which was America's largest economic expansion in a half century, barely peeked its head above the crowd. Of the 20 American high rises that reach 900 feet or more, none has been built in the past 10 years.
Meanwhile, nine have been built in China, and three each in the United Arab Emirates and Malaysia - with many others in the works. In the US, only the Trump Tower promises to enter that group in the near future.
One reason for the drop is a basic matter of ego. During the past decade, many of the great generators of wealth have not been steel magnates or shipping barons eager to enshrine their power in steel and stone, but rather high-tech companies that sprang from the progressive soil of Silicon Valley.
Here, corporate architecture reflects a different culture, as a more democratic workplace is spread out over landscaped campuses, rather than funneled up through fluorescent-lit floors to a top-level suite with leather chairs and an executives-only view.
Even for others in the business world, very tall skyscrapers have lost some of their appeal, simply because they don't make good economic sense. In high rises of more than 70 stories, the number of elevators needed to ferry thousands of people huge distances eats into available floor space, creating an equation of diminishing returns the higher a building climbs.
The only place that signature skyscrapers are booming is Asia. "[They've] still got that sort of swashbuckling mentality," says Stephen Goldberg, an architect in New York.
To some, that's not necessarily a bad thing. The Sears Tower and Empire State Building help define their cities - lending them an aspect of the unfathomable in their neck-craning height.
Mr. Goldberg, for one, looks back on the Golden Age of the American skyscraper with nostalgia. He remembers the construction of the World Trade Towers as an event beyond belief - a project that, in its massive scope, might have never been approved today. Yet it captured a moment of possibility.