Plans for buildings that are not just big but truly huge adorn the wails of Kohn Pedersen Fox (KPF), an architectural firm in New York. Few people aspire to 200 storeys. In the aftermath of the World Trade Centre"s collapse 18 months ago, such towering schemes seemed to have no chance of becoming reality. Yet in April KPF will complete work on a Tokyo complex with a central skyscraper that will feature one of the highest floors in Japan. Submissions are being readied for still bigger projects in several different countries. Whether "bigness" makes business sense is the subject of intense debate. Europe has largely stayed out of the skyscraper race. A proposed 66-storey London Bridge Tower, which would be the continent"s largest building, may eventually go up. It would not stand out in Manhattan. Executives in the City of London, Europe"s largest financial market, contend that even in a non-earthquake-prone area, once a building rises much above 50 storeys the demand for additional elevators, stairwells and structural supports makes them unacceptably inefficient. True, up to a point, says Paul Katz, the architect at KPF, but the most efficient building is not necessarily the most valuable. There are some explicit benefits from sky scrapers, notably efficient energy usage, plus less tangible ones such as the savings and benefits that come from clustering employees in one place. Typically, where firms most like to operate, sites are scarce. As a result, it often makes sense to add floors, even at ever greater cost. Skyscrapers have risen slowly in Japan due to earthquake fears, but now they are going up. With New York"s economy suffering, redundancies mounting and continuing fear of terrorism, it is hard to imagine anybody financing new construction in the city, let alone a vast new skyscraper on a site that many believe should be used only as a memorial. But even before the events of September 11th, construction techniques were changing to resolve shortcomings that existed in the 1960s when work began on the World Trade Center. Rather than being supported merely by steel curtain walls, the new skyscrapers have concrete cores linked to strong columns in the outer walls. Nobody now underestimates the devastation that would be caused if an aircraft strikes a building; but at the least, the new crop of tall buildings are designed so that they would not collapse if hit by even the largest passenger plane. That may not sound particularly reassuring to anyone asked to work on the 100th floor. But the business of building to the sky dates back at least to the tower of Babel—and no disaster has stopped it for long.