Remember this is an office building, and office buildings are usually very boring indeed. A glance at the new blocks at Paternoster Square by St. Paul's Cathedral is enough to confirm that view. There you find several leading architects recruited in the cause of extreme dullness. So if Foster can make offices interesting, he has done us a favour. Just stacking them up vertically is not enough. For instance another recent Foster tower, at Canary Wharf, is a standard commercial diagram and desperately anodyne as a consequence. But here, on the bomb-blasted site of the former Baltic Exchange, he has done what very few architects ever manage. He has, not for the first time, reinvented a building type. This is a new kind of skyscraper.

He was lucky to be presented with the best possible site, on London's medieval crossroads. This is why you see it from everywhere. But Foster has exploited this advantage superbly. And this is why the fine details of it aren't so important. Because the Gherkin has changed our view of London. It has made sense of what was previously an unsatisfactory skyline. It has not tried to be the tallest - it defers to the neighbouring NatWest Tower - but Foster's building has anchored everything. Its smooth circular, tapering shape is exactly right for this role as central pivot to the financial district. There it is, utterly distinctive. It orientates you.