>...but the millenium bridge was DESIGNED to wobble!<

Fairenoughsky Tuesday (though I doubt it was designed to wobble <i>quite</i> as much as it did nor the Kansai International Airport <i>sink</i> quite as much as it did. The point I hoped to make was that structures <i>are</i> inherently subject to the forces of nature and, one way or another, have to accommodate those forces (and Silbury is no exception).

It's quite interesting actually (well it is to me :-) just how much local climatic conditions dictate the shape of local structures - steeply pitched roofs in places of heavy snow fall, flat roofs in areas of little rain. The introduction of the arch to Europe revolutionised what could be done with space, freeing it up for domes, stained glass windows etc, while the flying buttress (a structural necessity) also evolved into something quite beautiful.

But just to get back to wobbling. Traditional Japanese architecture (which does not utilize the arch at all by the way) is designed to wobble during earthquakes - as are most modern structures in earthquake-prone areas of the world - well some areas of the world :-( The most spectacular example of a built in 'wobble factor' is the pagoda; this is built on a 'floating' foundation and is supported by a single wooden post set (but not fixed) in a stone slab - the post runs from foundation to finial and consequently dictates the maximum height a pagoda can be built.

Oh... and don't forget Tudor chimney stacks, and the reasons why they're so tall :-)