Just learned a 2,000 year old Roman concrete seawall in Naples is still holding back the ocean

Faith Chen · 2026-09-11T13:30:08.96984+00:00

I was reading about the ancient harbor at Caesarea and fell down a rabbit hole into Roman marine concrete, and the thing that got me is that they were mixing volcanic ash into it on purpose. There's a breakwater near Naples that's been sitting in salt water since around 37 BC and it's in better shape than some docks poured in the 1970s. Does anyone know if researchers ever figured out the exact ash to lime ratio they used, or is that still kind of a mystery?

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Just learned a 2,000 year old Roman concrete seawall in Naples is still holding back the ocean | Archaeology Discoveries - Guest Forum