Edit- After reading most of the comments the general consensus is listed below:
1. The unique composite matrix of the concrete used gives it a self-healing property. When cracks form in the concrete, it will naturally seal them.
2. The Pantheon was a very significant structure which led to meticulous maintenance and restorations
3. The Romans didn’t have modern engineering. So they didn’t know exactly how strong they’d have to build the Pantheon to make it last. Their solution was to overbuild the hell out of it.
4. Survivorship bias. There were thousands of buildings constructed by the Romans but very few remain which are the ones we marvel at.
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In: 564
To add to everyone else.
The pantheon actually did collapse partially after about 100 years- it was rebuilt.
It’s also been restored a *bunch* of times, by Kings and popes and emperors and Il duces and prime ministers.
People don’t really know why.
I read an article earlier in the week that reported on some new research which suggested that Roman concrete had an additional type of lime mixed into it, which when exposed to water (through cracks forming in the concrete) will expand and fill the crack “healing” the concrete. The researchers hypothesised that the healing lime was formed when hot mixing the concrete, and the article went on to suggest that further research into this could dramatically reduce the embodied carbon impact of building in concrete.
ELI5:
Roman concrete has a fancy type of lime in it
The lime heals the concrete when cracks form
Without cracks concrete lasts a lot longer.
Edit: someone below reads the same thing I do: https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106
There was a scientific test just done on Pantheon concrete. The Romans mixed calcium carbonate pebbles into it. So when water seeps in cracks the carbonate reacts and seals the crack. Self repairing. Just heard this on BBC World News podcast
https://open.spotify.com/episode/3Zn8M9HeflTMSSXJIk7fGd?
So a couple of reasons:
1: survivorship bias. You notice the buildings that are around. Not the ones that fell over.
2: it was a place of great significance meaning it for more attention and maintenence than Joe-relius’ Flatbread shop.
3: the method with which it was built and designed. The Roman’s didn’t have steel reinforcement like we do. Concrete on its own can’t really take any tension (things pulling it apart) but is really good at compression. Steel is the opposite. When you mix the two together like we do you get a material that is good at both tension and compression.
So the Roman’s had to build structures to always be in compression because of this. The only way to do that really is to use a very veery large amount of concrete. This means that Roman buildings are essentially just giant cast in place rocks and rocks last a really long time. There’s not much to rust or degrade like our new buildings full of steel and other new materials.
Basically comes down to the fact that concrete really likes being concrete and so doesn’t change much over the years but steel really doesn’t want to be steel so it tries changing as fast as it can.
Fun fact that no one will care about: a lot of Roman and Greek ancient buildings (ex. The Colosseum) are so decayed not because of poor engineering or lack of maintenance, but because they were literally dismantled to get marble and other materials to build new buildings.
Or because they were bombed during WWII, an occurrence that ancient Romans obviously didn’t think about.
That’s also the reason why a lot of medieval buildings are still standing, because they were not made with pricey materials but built well enough to survive centuries.
Imagine being the Pope and going like: “need marble? Just take it from the Colosseum, no one cares about that old sh*t”
The Pantheon is made of very large rocks. Most modern buildings are not made of very large rocks. If we build something out of very large rocks (and no one actively tries to knock it down), then something we build today is likely to stand for 2000 years.
Note: concrete is not a very large rock. Concrete is many small rocks.
believe it or not, houses last longer when people live inside of them regularly. the condensation prevents walls and foundations from crumbling to dust from drying out. it makes sense, as soon as you get a crack in a foundation any plant can start rooting and pushing the foundation apart.
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Every house within 3 miles of me is over 140 years old.
I live in Salford, Manchester UK.
Reasonably well built bricks and mortar lasts well with maintenance.
Mostly it’s about good roofs.
Pantheon is a concrete dome, pretty damn amazing from the outset, but it has been maintained and repaired, plus its got a great roof.
Wooden houses, poorly maintained, dont last long.
The high school built in my city back in 1890 is still standing, is beautiful, and is used as a courthouse today. It’s replacement, built in the 1970’s, was a farce of construction, and was demolished two years ago. But the builder still got paid for his shitty work, didn’t he? The new high school cost $150 million and will take 30 years for the homeowners in my city to pay off through increased taxes. I predict we will be having this exact same conversation in 30 years. Wanna bet? Modern capitalism doesn’t design or build for longevity. They build for profit. Nothing else. THIS is the American way.
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