So the stage is set for a big revival of vertical buildings. The most spectacular crop of new towers in the near future is going to be in the heart of the capital: in the City of London, where the money is. The skyline of the City had remained largely frozen since the 600 foot NatWest Tower, a 1970s design, was opened in 1981. Younger-generation commercial palaces - even those as grand as Richard Rogers' high-tech Lloyd's of London, designed in 1978 and opened in 1986 - kept relatively low and squat, hunkering down. Lloyd's is high at 312 feet, but not skyscraper-high. Many others literally dug themselves into the ground. Leftover tower plans from an earlier era were ceremoniously torn up. It was the era of the groundscraper, the football-pitch-sized City dealing floor. Despite occasional publicity-seeking plans for great towers in other British cities, these also came to nothing. In London as in Paris, tall commercial buildings were pushed to the perimeter - in our case, eastwards to Canary Wharf in the abandoned former docklands, where unbridled market forces combined with irresistible tax breaks showed what commerce really wanted: tall, prestige, readily-identifiable buildings of the kind the City had given up trying to provide. There things rested. Until the arrival of the Gherkin.

Officially known as 30 St Mary Axe, this sleek tapering circular office tower, designed by architect Lord Foster, was, like the redevelopment of Central Manchester, made possible by the previous attentions of the I.R.A. The huge terrorist bomb blast that took place on an April evening in 1992 had devastated a vast swathe of the City, largely destroying the old shipping brokerage, the Baltic Exchange. The relatively tight site of the Exchange, right at the medieval crossroads of London, demanded a response that was different from usual. No squat groundscraper would fit here - and firms had abandoned vast dealing floors anyway. Other buildings hemmed it in closely. Foster's first attempt here was a 1996 scheme for a skyscraper like an enormous pronged stick of celery rising to 1,076 feet (the prongs being apartments above a lower section of offices, on the American model). That was too much, too soon, for Britain. Nor was it Foster's most convincing design.

So the site was sold on to Swiss Reinsurance, an outfit with high architectural standards. Foster and his team engaged with reality, went straight back to the drawing board in 1997, and sketched out an idea that was brilliantly simple: a tall building, but at 590 feet not too tall, and moreover one that sat lightly in its socket. One that tapered towards the bottom as well as the top, so allowing a public square around the base. One that was circular, so that the wind slipped round it rather than bouncing down the façade and blowing people off their feet. One with an external diamond latticework structure and a delicate glass nosecone. And one that, placed where it was, would be seen from all directions right across the capital. A lynchpin for London. They started building it in 2001, and it is just finished. It works. Just about everybody loves the Gherkin. And it changed everything.