Roman Concrete

Roman concrete, known to the Romans as opus caementicium, is a hydraulic building material made from a lime-based binder mixed with volcanic ash, most famously from deposits near Pozzuoli, and aggregate, developed and refined across the Roman world from roughly the third century BCE onward. Its use enabled monumental unreinforced structures still standing today, including the coffered dome of the Pantheon and the harbor works of Caesarea, and modern research has traced its exceptional long-term durability, including a documented case of self-healing through mineral crystallization in seawater exposure, to the specific volcanic-ash chemistry and hot-mixing techniques the Romans employed, properties distinct from and in some respects superior to ordinary modern Portland-cement concrete.