There's also the still open question on how the pyramids of Egypt were built, and AFAIK NASA lost the knowledge how to build some stuff as well. And the recipe

There's also the still open question on how the pyramids of Egypt were built, and AFAIK NASA lost the knowledge how to build some stuff as well. And the recipe for Roman concrete was also long lost, with researchers being able to reverse-engineer what it likely was only a few years ago [1]. [1] https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106 https://news.mit.edu/2023/roman-concrete-durability-lime-cas...