For the first time, researchers have identified exactly what Roman builders were adding to their concrete to make it last for centuries....

For the first time, researchers have identified exactly what Roman builders were adding to their concrete to make it last for centuries....

At an unfinished building site in Pompeii, abandoned during the eruption of Mount Vesuvius in 79 AD, archaeologists uncovered something rare: Roman concrete materials that were prepared but never mixed. That frozen moment revealed how Roman builders actually made their concrete.

Instead of mixing lime and water the way we do today, they combined quicklime with volcanic ash first, then added water. The reaction produced intense heat and left behind tiny fragments of reactive lime trapped inside the hardened concrete. When cracks later formed and water seeped in, those fragments reacted again and sealed the damage from within.

In other words, some Roman concrete was intentionally engineered to heal its own cracks — and it’s still doing it nearly 2,000 years later.

Archaeological Park of Pompeii