And, slightly before that, between 23 and 15 BCE, Herod instructed his engineers to build this harbour - claimed as the largest ever built (to that point in time)
(See aerial view of the harbour at Link, and notes at : http://web.uvic.ca/~jpoleson/ROMACONS/Caesarea2005.htm )
Named Sebastos (the Greek equivalent of Augustus), the harbour of Caesarea Palaestine, also known in Greek as Caesarea on the Sea,was founded on a shifting sand beach devoid of any mitigating physical features. The shoreline was exposed to the longest fetch in the Mediterranean and scoured by a strong long-shore current that carried sand from south to north. The site had been selected primarily for political reasons, not because nature favoured the construction of a port at this location (Holum and Hohlfelder 1988). Once the royal decision had been made, it was up to King Herod’s builders to execute his desires, even though they faced design and construction challenges never before encountered by Mediterranean harbour engineers (Hohlfelder, 2000 and 2003). Underwater excavation and exploration have been carried out in the submerged ruins of Herod’s vast harbour complex almost continuously since 1960 in an effort to understand how this daunting ancient engineering project was executed so quickly and expertly in the face of seemingly insurmountable obstacles. The bibliography on the underwater excavations at Caesarea Palaestinae is considerable. Most published works relevant to this article are listed in the references section of Oleson et al. 2004, 228-9. This archaeological research has produced a vast literature that has revealed some, but not all, of the secrets of Sebastos.
Since 2002, the Roman Maritime Concrete Study (ROMACONS) has been conducting fieldwork in Italy, collecting cores from maritime structures constructed of Roman hydraulic concrete, and building an underwater reproduction of a pila or pier using materials and tools that would have been available to Roman builders (Oleson et al., 2004a, 2004b; Hohlfelder et al., 2005; Oleson et al., 2006). So far, we have collected cores from Roman maritime structures at Portus, Anzio, Cosa, Santa Liberata, and Baia. Roman hydraulic concrete consisted of a mortar made from lime, pozzolana (a sand-like volcanic ash naturally rich in aluminosilicates), and water, to which various types of rubble aggregate was added. The resultant mixture was a hard and durable concrete that could solidify underwater