[freebeard]

Vitruvius, writing around 25 BC in his Ten Books on Architecture, distinguished types of aggregate appropriate for the preparation of lime mortars. For structural mortars, he recommended pozzolana (pulvis puteolanus in Latin), the volcanic sand from the beds of Pozzuoli, which are brownish-yellow-gray in color in that area around Naples, and reddish-brown near Rome. Vitruvius specifies a ratio of 1 part lime to 3 parts pozzolana for cement used in buildings and a 1:2 ratio of lime to pozzolana for underwater work, essentially the same ratio mixed today for concrete used in marine locations.[4]

By the middle of the first century, the principles of underwater construction in concrete were well known to Roman builders. The city of Caesarea was the earliest known example to have made use of underwater Roman concrete technology on such a large scale.[5]

https://en.wikipedia.org/wiki/Roman_concrete