Perhaps it's the weather, which sometimes seals London with a gray ceiling for weeks on end. Or maybe it is Britons' penchant for understatement, their romantic association with the countryside or their love of gardens. Whatever the reason, while other cities grew upward as they developed, London spread outward, keeping its vast parks, its rows of townhouses and its horizon lines intact. But as the city's population and its prominence as a global business capital continue to grow, it sometimes seems ready to burst at the seams. In response, developers are turning to a type of building that used to be deeply unfashionable here, even as it flourished in other capitals of commerce: the skyscraper. In recent years, a cluster of sizable office towers have sprouted on the periphery of London, in its redeveloped Docklands at Canary Wharf. But skyscrapers now are pushing into the heart of the City, London's central financial district, and surrounding areas along the Thames. The mayor, Ken Livingstone, champions tall buildings as part of his controversial plans to remake central London as a denser, more urban sort of place, with greater reliance on public transport. First he angered some drivers by charging them a toll to enter the city center on workdays, now he finds himself opposed by preservation groups, including English Heritage, that want to keep London's character as a low-rise city. For now, the mayor seems to be getting his way. One prominent tower, a 40-story building designed by Norman Foster for the Swiss Re insurance company was completed this year. A handful of others have received planning permission and at least a dozen mere have been proposed. By far the most prominent of these buildings—and one that finally looks like it will go ahead after a drawn-out approval process—is the London Bridge Tower, designed by the Italian architect Renzo Piano. The developer Irvine Sellar won government approval for the building late last year and says he is completing the financing and hopes to start work by early 2005. The 306-meter, or 1,016-foot, tower would be by far the tallest building in Britain, in all of Europe, in fact, surpassing the 264-meter Triumph Palace in Moscow, a residential building that was finished late last year. To be sure, even the London Bridge Tower would be modest by the standards of American or Asian skyscrapers, or some of the behemoths on the drawing hoards for places like Dubai and Shanghai. The tallest building in the world at the moment is the 509-meter Taipei 101 tower in Taiwan, according to the Council on Tall Buildings and Urban Habitat. But it will surely be surpassed soon amid a boom in construction that persists. In a city that has been reluctant to reach for the sky, perhaps it is appropriate that Piano is the architect for what probably will be London's tallest building. He is ambivalent about skyscrapers, too, and has designed only a handful alongside such projects as the Pompidou Center in Paris, with Richard Rogers, and parts of the reconstructed Potsdamer Platz in Berlin. English Heritage has been far less enthusiastic, arguing that the building would obstruct views of a high-rise from a much earlier era, Christopher Wren's St. Paul's Cathedral. To overcome opposition, the building was designed with a mixed-use function. Much of the bottom half of the building will house offices, but above that there will be a 'public piazza' with restaurants, exhibition spaces and other entertainment areas. Further above, the loftier, narrower floors will be taken up by a hotel and apartments. On the 65th floor there will be a viewing gallery. The upper 60 meters, exposed to the elements, will house an energy-saving cooling system in which pipes will be used to pump excess heat up from the offices below and dissipate it into the winds. 'We knew we had no chance of getting it approved unless we had a high-quality design