[PIF]

Cement - perhaps their most advanced and enduring contribution to building - only equaled in recent years.

[pierrem15]

Yup- forgot about that. Only it wasn't enduring in the sense that the secret of producing the volcanic cement produced by the Romans died with the Empire.

I believe that cement not only sets under water but also has a tensile strength more or less equal to our reinforced concrete, without the reinforcement.

I think there's a company in Arizona or New Mexico that is marketing a similar concrete made from American volcanic material.