I once watched a travel documentary with Griff Rhys Jones in Paris, where he meets an underground group of people that sneak into official buildings at night and repair things, they apparently have access to pretty much every building in Paris:

https://www.youtube.com/watch?v=nLkl0r0C1ro (Section starts at 36m in)

Maybe they're already repairing it?

A small counterpoint; structures made of a weathering steel, like COR-TEN, don't need to be painted. The trade offs include ensuring the welds weather at the same rate as the structure and needing a salt alternative for de-icing in the winter.

The most prominent example I know of is the New River Gorge Bridge in West Virginia.

Weathering steel can still corrode to the point of collapse, e.g. the Fern Hollow Bridge.

Golden Gate bride has a crew whose only job is to paint it. Again and again and again.

That’s all they do. Repaint it.

Kind of give you an idea of how important maintenance is.

I’m still not certain why all those Roman bridges are still around though.

Overengineered things will tend to survive. Since they didn't really know how gravity/structural forces work, they would have made some bridges with too much reinforcement and some with too little.

You end up seeing the survivors. Luckily they are also not made of something requiring maintenance like metal.

Your conclusions about what the Romans did and did not know seem dubious. Even in the modern era we still fuck constructions up, despite all we know.

If I recall correctly they had pretty strict standards for the roads themselves [citation needed], I would suspect much the same existed for bridges. Having said that, I think it stands to reason that chemical processes and variances in materials locally sourced would be something worthy of scrutiny. Porting tons of materials in those days would be suboptimal to say the least, so concrete compositions could suffer, alongside with a litany of other material compromises. Add in process errors and I think it becomes a far more compelling hypothesis than "they just slapped shit together but somehow invented keystones, leveraging both structural and gravitational forces"

Knowing what we do know, I think, tends more towards material optimization. We can more confidently design structures and do it with greater respect to cost - something I don't know that earlier civilizations paid a lot of mind to, especially when looking at the multi-decadal constructions of cathedrals for instance or more on point the coliseum.

> Even in the modern era we still fuck constructions up, despite all we know.

That's precisely why we fuck it up, because we know tolerances and such much better, and we can do things with much finer granularity. So we aim to build right at that precise edge of "just barely above what's minimally required for it to work." And when small fuck ups happen, that edge gets lost, and suddenly it is all falling down.

In Roman times? No precise tools and techniques were available, things had far less granularity. So when they decided they wanted to build things "good enough", there was no precise edge. They would often ballpark for a construction project to be much stronger than minimally needed (by modern measurements), precisely because that "minimally needed" wasn't nearly as simple to achieve or even calculate.

Think about medieval brick castles. Some are still standing, while some houses built only about 100 years ago are pretty much disintegrating. Is it because we don't know how to build castles anymore? Not at all, it's just we try to build on the edge of the calculated expected lifespan of a house, balancing pricing at the same time. It was extremely difficult to do something like this with the knowledge available back then, so if they wanted something actually stable, they would often go for an overkill.

My argument is the the Romans had a really good understanding of the macro forces, but minimal knowledge of the micro forces. I would also expect long-run events would be more difficult to parse. The floodlines of Egypt, for instance, required a modern engineer decades of work to model because there is a complex system of dependency undergirding the processes determining them. Prior years flooding determined the latter years, this wasn't integrated into the reasoning when it came to constructing dams, instead they used 100-years floodlines to determine how high to build the dams, which was inadequate for the safety margin. I suspect such errant features of nature might explain failures, and material issues, but I'm definitely confident Romans had a highly intimate understanding of the high-visibility macro forces, because you really just can't miss broken sticks and falling bricks, can you?

Many of the castles (“Kracs”) used by the Crusaders still exist. They were used as military forts during the recent war.

They stood up very well.

Think about that … even against modern artillery, they still held. And with little damage.

The Romans considered bridge building to be a religious activity. Rivers were gods, and bridges interfered with them.

A crappy bridge was sacrilegious.

Similarly, the iconic Forth Rail Bridge in Scotland used to be repainted almost continuously.

However, a decade ago they repainted it using more expensive paint, which should last two decades.

Because they are made of concrete and not of iron.

It sounds like the concern is less the repair expense and more the time that the tower would have to be closed and the loss of tourist revenue.

The lost revenue you describe is just one part of the repair expense, it is not separate

A giant tent and sand blasting. It’s going to have to happen eventually… the delay just makes things worse