I saw an article a while back about the unique properties of ancient Roman cement. It seems that the sea water hitting the walls created a rare mineral when due to a chemical reaction.

https://www.nature.com/articles/nature.2017.22231

I often wonder about how things are built without preservation/archival in mind. We live in an age where so many things are built in so much faster than the past but, with the expectation that they will be replaced even faster than in the past.