[otikik]

Not necessarily countering your point, but perhaps giving some perspective.

The City I grew in (Cordoba) has a roman bridge[1], originally built 1st century BC and still standing. It supported a 2-way street until 2004, when it was pedestrianised.

Caveats:

* It has gone over a great deal of renovations/partial rebuilds on its history, so its durability can not really be attributed to roman concrete alone. Only 2 of the original 16 arcades remain. One could argue that "it's not the same bridge" any more (Theseus' Bridge).

* I ignore wether they used concrete to build the original one. I'm not an architect. For all I know, the initial construction could have been mortarless stone, and cement (as well as reinforcement) could have been added in some of the later renovations.

That said, all bridges require periodical servicing/renovations anyway, in order to remain functional. And this one has stand for 2000 years.

[1] https://en.wikipedia.org/wiki/Roman_bridge_of_C%C3%B3rdoba

[masklinn]

This doesn’t really give perspective, it’s basically what they’re saying. Roman bridges are gravity structures, the entire thing is in compression and heavy, the arches have really limited spans.

Compare to the Millau Viaduct for instance.

[otikik]

Well in order to compare things properly we would have to check if the Viaduct is still there 2000 years from now.

[masklinn]

That's a completely different axis is the point, you can not solve the issues the viaduc solved, let alone build anything even remotely similar, using roman materials (to say nothing of techniques).