"Why do I love Paris?" Cole Porter keeps asking, in one of his least clever songs. "Why, oh why, do I love Paris?" Finally he ends the suspense. It's because his sweetie is in the neighborhood.

The really intriguing question is why everybody else loves Paris, even when they are not overcome by infatuation. I've never met anyone who wasn't taken with the city, and that includes people who don't care for the French. I'll be honest: I like Paris quite a bit myself.

But deconstructing the city's magic isn't so simple. It doesn't have a scenic setting, like San Francisco or Rio. It doesn't have great weather; even Cole Porter admitted that it had a tendency to drizzle in winter and sizzle in summer. Its monumental public spaces are choked by traffic, and its streetscape is a little monotonous compared to that of Rome or London or even Boston.

True, there are some pleasant amenities: trees on the boulevards, flowers in the upstairs window-boxes, and the curiously intense sunlight that artists have come from all over the world to experience. But those qualities wouldn't seem sufficient to create the "world's most beautiful city." There must be another reason.

Walk around long enough and you begin to think about what it might be. All those boulevards lined with five-story gray stone buildings may lack the architectural variety that other cities thrive on, but they produce a compelling combination of order, stateliness and human scale. Walking the streets of Paris, James Howard Kunstler writes in his book, "The City in Mind," creates "a tremendous sense of satisfaction that you are finally in a human habitat that completely makes sense."

Kunstler may overdo things a bit, but it's undeniably the case that Paris looks like a city designed by someone who knew what he was doing--who had an idea and carried it out. And of course, that's what it is. The Paris that everybody loves was built in the mid-19th century by Baron Georges Haussmann, the planner endowed by Napoleon III in the 1850s and '60s with the money and authority to rebuild the capital city of France virtually any way he chose.

It's almost impossible to think about Haussmann and Paris without drawing a comparison to Robert Moses, New York's master planner of the mid-20th century. The circumstances were totally different: Haussmann was granted power by an emperor; Moses seized it through bureaucratic gamesmanship. But they were both planner-kings, perhaps the only ones who have existed in any major world city in modern times.

One of them built a hideous jungle of freeways and high-rise housing projects from which an entire region has yet to fully recover. The other built a graceful city whose elegance seems only to grow with the passage of time.

The Parisian elite didn't realize at first what Haussmann had accomplished. In the early period after his projects were complete, they accused him of tearing up neighborhoods, uprooting thousands of residents, and replacing quaint old houses with endless rows of sterile apartment buildings. Essentially, they said the same things that people today say about Robert Moses.

The one difference is that, before too many years had elapsed, the criticism of Haussmann had subsided; even the skeptics began to concede that he had created something beautiful. Even if we wait another century, I doubt if anyone will be saying that about the Cross-Bronx Expressway or the Bushwick projects in Brooklyn.

Perhaps Haussmann was blessed with superior aesthetic sensibilities, but I doubt it. I do know that he had one circumstantial advantage. He couldn't build anything very tall. The technology wouldn't allow it. The steel-frame construction that made skyscrapers possible hadn't been invented yet, and in any case, there were no elevators. The maximum height of a building corresponded to the number of stairs an ordinary human being could be persuaded to climb. More than five flights was considered an imposition. And so Paris became a five-story town.

This may have been an accidental achievement, but it's a great achievement nevertheless. If you're in the habit of walking down boulevards, in Paris or any other city, you've probably noticed that a row of one- and two-story buildings is too small to create much sense of grandeur, and a row of 20-story buildings is normally too big. It overwhelms the average pedestrian. Somehow five stories is just about right.

I know very little about architecture, but I do know that height matters. It is possible to have elegant boulevards of tall buildings-- most people like Fifth Avenue--but more often height seems to make a street uninviting. Urban planners have realized this for a long time. Almost as soon as it became feasible to create tall buildings in the United States, city councils began passing height limits to stop them.

Boston passed a limit of 125 feet (roughly 10 stories) in 1891 and stuck with it until the end of the 1920s. Scholars tend to attribute the persistence of this ordinance more to the self-interest of people who owned short buildings, and didn't want competition, than to any special aesthetic sensibility. But the law had a definite impact--it essentially prevented Boston from having any identifiable skyline until long after World War II. Buildings in Washington, D.C., were limited to 160 feet by act of Congress in 1901, and that limit remains in place today, which is why I can look straight out the window from my desk on the 13th floor and see nothing but rooftops at eye level. In Washington, 13 or 14 floors is as high as any building gets.

In most places, however, height limits didn't work. Chicago, for example, enacted a limit of 130 feet (about 10 stories) in 1893, but it provided for exceptions in special cases. The city's aldermen were more than willing to grant exceptions almost anytime the price was right. And as the urban scholar Robert Fogelson has documented, most local governments were more like the one in Chicago than like those in Boston or Washington. If they didn't have skyscrapers by the end of the 1920s, it was because nobody could be induced to build them.

European cities, Paris included, had an entirely different experience. Whether for reasons of legal limit, informal consensus or just market economics, they chose not to line their downtowns with skyscrapers even when it became technically easy to do so. As late as the 1950s, Fogelson points out, most big cities in Europe didn't have a single building more than 80 feet high. In 1929, there were more 10- story buildings in Beaumont, Texas, than there were in London or Paris.

That didn't last forever, of course. In the 1970s and '80s, even Paris began to show a fascination with building vertical monstrosities. Beyond the periphery of the central city, they now exist in virtually every form: office buildings, luxury apartment towers and hideous public housing projects. But that's the suburbs. Within the traditional urban core, Paris looks very much the way it did a century ago.

And so do most European cities. They have junked up the outskirts almost as badly as we have. But they have found ways to keep the center at human scale. For all the development that has taken place in recent decades, the competition to build ever taller is one that most cities in Europe have chosen not to enter. Of the 100 tallest buildings in the world right now, only two stand on European ground (numbers 67 and 71, both in Frankfurt).

It's hard not to see this as reflecting cultural difference. I haven't done a survey, but it seems to me most Americans believe that if something is technologically feasible, it will be done before long- -and, not only that, it should be done. Europeans have been much less likely to think so.

There's some reason to think this has changed a bit in recent years, at least when it comes to architecture. We aren't as enthralled with setting height records as we once were. In the mid-1980s, the 10 tallest buildings in the world were all in the United States. Now, only two are--the Empire State Building and the Sears Tower in Chicago. Of the 20 tallest built in the last decade, not one is in this country. Most are in Asia, in cities such as Shanghai, Hong Kong and Kuala Lumpur.

There are many reasons why this has happened. Corporations have downsized, employees can work from home, and so the demand for office space isn't what it once was. Still, it's reasonable to argue that there's a cultural component as well: We just aren't as enamored of gigantism as we used to be. Few planners, architects or politicians seem interested in defending the principles of height and bigness just for their own sake.

Nevertheless, the events of September 11, 2001, resulted in a national dialogue on this issue. When that day began, the 110-story twin towers of the World Trade Center carried the same negative reputation that had burdened them since their completion in 1973: They were sterile, oversized, slightly embarrassing monuments to a dead era in American architecture. By the time the day was over, they had been reborn as symbols of American pride and technological sophistication.

Under the circumstances, critics of gigantism might take comfort in the fact that few seriously considered replacing the fallen towers with anything nearly as large. On the other hand, the design eventually approved for the Trade Center site--Daniel Libeskind's complex of five buildings, each 50-70 stories high--doesn't exactly reflect a return to human scale, either.

Of course, there never was much doubt that whatever succeeded the World Trade Center had to have skyscraper quality. Replacing a pair of megatowers with a network of low-slung, tree-lined boulevards would have been ludicrous in lower Manhattan. For a whole variety of reasons, you just can't do it Haussmann's way anymore.

In the end, maybe that's the simplest and most compelling reason to love Paris: It's no longer possible to make one.