Back to the Future? - Rediscovering Roman Engineering in the Mediterranean Sea

Throughout the Mediterranean Sea, scores of ancient marine concrete monuments, once components of artificial harbors constructed by Roman builders as part of their vast imperial maritime infrastructure, have survived for two millennia and counting. Modern marine concrete usually survives in the sea for little more than 50 years and sometimes even less. What did Roman builders know that modern harbor engineers do not? This was one of the questions that the Roman Maritime Concrete Study, an international, multidisciplinary project that I organized and co-directed in the first decade of this century, hoped to answer. Field work was undertaken to collect and analyze concrete cores extracted from submerged and awash structures at various ancient harbor sites in Greece, Italy, Cyprus, Israel. and Egypt. The results of this study were published in BUILDING FOR ETERNITY: THE HISTORY AND TECHNOLOGY OF ROMAN CONCRETE ENGINEERING IN THE SEA, Oxford, 2014 and 2021.

The key ingredient responsible for the amazing longevity and resilience of Roman marine concrete (RMC) was volcanic ash or sand from the Bay of Naples (pulvis puteolanus). It was the binding element in the mortar that, along with aggregate, comprised the concrete itself. This Neapolitan volcanic ash has a unique chemical composition. When it was mixed with quick lime and seawater to which rock aggregate was added, the resulting concrete could be placed while still in a liquid state into the sea within a variety of wooden formworks to set quickly and then cure over time. The internal chemical processes that occurred as the concrete cured underwater eventually reduced the surface porosity until it became like rock itself. Moreover, these elements enabled any cracks that might occur in a RMC block to self-heal. Some material scientists have claimed that RMC may be the most durable substance yet created by humankind.

Speaker: Bob Hohlfelder, University of Colorado, emeritus

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