How Did Humans Invent Cement?

How Did Humans Invent Cement? The Pantheon has been standing for nearly nineteen hundred years. Its dome — still the largest unreinforced concrete dome on Earth, spanning forty-three point three meters from edge to edge, roughly the distance between home plate and second base on a standard baseball diamond — was poured without steel reinforcement, without modern quality control, and without any chemist present who could have explained, at the molecular level, why the material worked. The builders who mixed it could describe the proportions. They could tell you which volcanic sand to use and which harbors to ship it from. What they could not tell you was what was actually happening inside the material as it hardened, because that answer would not arrive for another nineteen centuries.