The history of exotic cement is so relevant that people are still studying its durability, centuries upon centuries later.
The secret of Roman cement was the mixing of lime with pozzolana, called harena fossicia or “pit sand” by Vitruvius. Pozzolana was distinguished from river and sea sands (the common harena) and receives this contemporary name from the town of Pozzuoli (Roman Puteoli, neighboring Baiae) in the Bay of Naples, just 25 miles east of Mt. Vesuvius. The entire region is heavily covered with meter thick beds of pozzolana, volcanic pumice and ash from previous eruptions.
In addition to Pozzuoli, Vitruvius mentions deposits of pit sand at Mount Aetna and there is evidence indicating the Roman exploitation of German trass, a sedimentary stone of lightly compacted volcanic ash having similar properties. Although the Romans typically are credited with inventing pozzolana-based cement, there is archaeological evidence that the Greeks were using their own pozzolana from the eruption at Thera (Santorini) for water cisterns as early as 600 B.C., as well as for methods of wall construction only later adopted by the Romans.