Since all long-distance trade in the Roman world travelled by water, Roman harbour design and construction have special importance. Harbour excavation must be supplemented by analysis of the components of the hydraulic concrete, structural analysis of the cementing materials, and consideration of the design of the wooden formwork. The authors have begun collecting large cores from concrete blocks at Roman harbours and other maritime structures, analysing the materials used, the method of placement, and the structural characteristics of the resulting concrete. These data have provided new information on the engineering properties of Roman concrete, the process of funding and execution, and the trade in the volcanic ash which was the crucial component of hydraulic concrete.

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The authors have completed structural and compositional analysis of Roman hydraulic concrete using large cores taken from a variety of maritime structures. In 2005 an 8 m 3 block of hydraulic, pozzolanic concrete was built in the sea at Brindisi (Italy), applying the materials and procedures specified by the Roman architect Vitruvius. Cores were taken at 6 months and 12 months after construction and subjected to the same analyses as the first-century BC cores from pilae associated with the Villa of the Domitii Ahenobarbi at Santa Liberata. Results show that a slight variation on the Vitruvian formula yields results closest to the Roman material, and that substantial curing requires 12 months.

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