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

Nobody seems to mention this.

The biggest component is Rebar.

Our modern concrete is *significantly* better than Roman concrete because of reinforcement. The cost of this is that the iron rusts, and as it rusts, it expands, and as it expands, it cracks the concrete, which lets it rust more, which causes the death spiral.

Modern concrete is only supposed to last ~50 years because of a design decision. We would be more than capable of building a building that will last 2000 years, that’s just never a design requirement.