How is it that Roman buildings “heal” themselves?

Question

Saw an article or documentary and it said something to the effect of Roman buildings heal themselves after being damaged or weather damage.

How can that be

In: Engineering

Answer 1

https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106

Roman concrete included reactive calcium bits and was mixed hot. Google “self healing Roman concrete” if you want to read any of the research published in the last couple of years.