Michael Jennings has a nice photo essay about the new viaduct in France:

The materials from which this bridge has been built are vastly stronger than anything that existed even 20 years ago. I have said this before, but this is in my mind the defining characteristic of modern post materials revolution structural engineering. Structures are then, flimsy. They almost look like spider webs. The defining characteristic of industrial age engineering was bulk. But now we are in this virtuous circle of stronger and lighter materials allowing a much thinner deck, allowing the other parts of the bridge to be lighter and less substantial too, allowing still more economies elsewhere, and a rapidly dropping cost of projects like this.

That will be a characteristic of a space elevator as well, if it's built.

I don't see spiderweb-like structures lasting well in the long-run though. The thing about brick, stone and concrete is that they last for thousands of year. Check out some of the Greek and Roman stuff...

They last for thousands of years, except for when they don't. A great deal of stuff from that age has disappeared. And the stuff that survives isn't in terribly good shape.

"That will be a characteristic of a space elevator as well, if it's built."

What do you mean _if_? (grin).

If you make your structures too light without understanding all the implications, you run the risk of building the next Tacoma Narrows Bridge.

Hey Raoul, as long as we get some cool video of it shaking apart, and no one's on it when it happens...

Just kidding.

I think the longevity issue mightr be real, The massive structures of the Brooklyn Bridge is over 100 years old. I can't envision some of these lighter weight bridges lasting as long