MAGNETIC DETECTION OF SUBMERGED HARBOUR STRUCTURES AND ANCHORAGES IN KING HEROD'S HARBOUR, CAESAREA MARITIMA, ISRAEL

A marine geophysical survey was conducted at Caesarea Maritima, Israel, to map the buried structure of King Herod's Roman harbor. 107 line km of magnetic and bathymetry data were acquired over a 1 km² area of the submerged harbour. Magnetic surveys reveal the presence of an extensive hydraulic concrete foundation below the ruined harbor moles. The magnetic anomaly patterns show that the concrete foundation was laid out in header fashion along N-S and W-E trending segments to form two large ‘artificial islands'. Magnetic lows within the structure identify baffles that were in filled with sand to stabilize the concrete foundation walls. Investigations of the area seaward of the harbor identified a large (ca. 100 m dia.) circular magnetic anomaly that has bathymetric expression as a low-relief mound. Jet-probing and excavation of mounds at 7 locations revealed a 20-50 cm thick rubble layer consisting of boulders with abundant pottery fragments. The boulder materials include and local sedimentary bedrock, wadi cobbles and abundant granitic and metamorphic rock types foreign to the Levant. The presence of extra-basinal materials identifies the rubble layer as ballast dropped by ships in preparation for loading of cargo. Radiocarbon dating and pottery evidence indicate that the ballast was accumulated beginning in the Late Roman period (ca. 300 AD). The large volume of ballast within the mounds suggests a sustained use of the inshore area seaward of Herod's harbor as a lighting and anchorage area. These new data are consistent with other geoarchaeological evidence that points to the rapid demise of Herod's harbor in the late 1^st- to 2^nd-century AD and a limited capacity to function as protective anchorage after that time.