caementum, -ī [2/n]: unhewn stones from a quarry; Vitruvius (Roman architect 1st c. BC) refers to caementa marmorea: chips of marble i.e. pieces that fly off during the quarrying process.
The stones or rubble were used as an aggregate (coarse material such as gravel or crushed stone for the purpose of construction). This was mixed with lime (produced by heating limestone), volcanic ash and water. For structural mortars Vitruvius recommended pozzolana (La: pulvis puteolānus) the volcanic sand from Pozzuoli near Naples.
The chemical reaction gave Roman concrete tremendous durability: aqueducts, the Colosseum and the Pantheon are still standing – 2,000 years after they were constructed. And so, perhaps one commentator is right when he says it is “a candidate for the most durable building material in human history".
caementīcius, -a, -um: consisting of / pertaining to quarried stones
caementīciae strūctūrae: concrete structures i.e. those formed with quarried stone aggregate
opus caementicium: Roman term for concrete
https://en.wikipedia.org/wiki/Roman_concrete
https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0062:entry=caementum-harpers
https://en.wikipedia.org/wiki/Pozzolana
The link below gives good information about the building materials used in the construction of the Colosseum:
https://colosseumrometickets.com/building-materials-of-the-colosseum/
