Why are ancient buildings still standing 1500+ years later, but some buildings built like 30 years ago are falling apart?
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Survivorship bias
Most of the buildings from centuries ago have long since been destroyed. The ones that are still around today are the ones that were really well build or had extraordinary steps taken to preserve them or were just lucky.
Most buildings build in the last 20 years will fall apart or be destroyed sooner or later, but some will last longer than others.
If you check back in a few centuries on surviving buildings from the first quarter of the 21st century, you will probably think that they don’t build them like they used to when comparing them to then current buildings.
There is an additional issue that some building methods come with inherent downsides. Reinforced concrete is really cool, but simply will not last as long as just piling some sandstone blocks on top of each other.
Also modern engineering allows you to build structures just strong enough to last as long as they need to. Without being able to simulate some things you had to add a far greater margin of error.
Because they built things to last back then, now they build it to only last a fraction of the time.
1. Survivor bias
2. Old buildings that are still around are made from thick stone, pretty much perfect to stand the test of time.
3. For hundreds of years we’ve actually been maintaining these older buildings, doubly helping them stick around
Fun fact time – If you live in America, my house is older than your country.
Not all 1500+ year old buildings are standing, in fact vast majority of them have collapsed ages ago. Only the rare ones that were built a certain way and cared for well enough are left.
One thing most remaining ancient structures have in common is that they are built to only withstand compressive stress. A pyramid is already a pile of rocks, what is supposed to happen to it? It can’t exactly tip over.
The problem with compressive structures is that they are very inefficient in terms of space and cost. For example the very old ones that predate invention of proper arches had to resort to this sort of thing: [https://www.magzter.com/stories/Education/Ancient-Egypt/The-Monumental-Vaults-in-Pyramids-A-Major-Technical-Challenge](https://www.magzter.com/stories/Education/Ancient-Egypt/The-Monumental-Vaults-in-Pyramids-A-Major-Technical-Challenge) They did not know how to make a flat ceiling in such a place so that it wouldn’t collapse. They didn’t even know how to make arches (ancient aliens and forgotten advanced civilizations my arse).
Something more romanesque would heavily use arches, making for much lighter structures with much more of the volume being actually usable [https://en.wikipedia.org/wiki/Romanesque_art#/media/File:Leon_(San_Isidoro,_pante%C3%B3n).jpg](https://en.wikipedia.org/wiki/romanesque_art#/media/file:leon_(san_isidoro,_pante%c3%b3n).jpg)
In contrast, modern modern buildings are basically all usable volume and the amount of material used is next to nothing. [https://www.designingbuildings.co.uk/wiki/Concrete_frame](https://www.designingbuildings.co.uk/wiki/concrete_frame) The cost of it though is that the floor panels are all under tension, the rebar in the concrete is what’s holding it together, without that composite structure it would be impossible to build like that. It also means that such structures will not last forever, a building is experiencing dynamic loading from all sorts of sources and that means the rebar will fatigue and the concrete will eventually fail. There will be no thousand year old skyscrapers.
survivor bias
most of the buildings built 1500+ years ago are not still standing. there’s a number of buildings we built today that will probably be standing in some form or another in 1500 years
It depends where too, places with extreme weather or seismic activity. But older buildings you still see many have been restored and they are made of granite, marble, stone not like modern buildings
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