How the Pantheon, which was built over 2000 years ago, is still standing when buildings made 150 years ago are about to crumble.

Question

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

Answer 1

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.