A Marine Geophysical Survey illustrates Alexandria's Hellenistic Past

摘要

The combined interpretation of the detailed bathymetric, sub-bottom profiling and side scan sonar data acquired offshore the Eastern Harbour of Alexandria, revealed evidences for the reconstruction of the coastal geomorphology of Alexandria at the Hellenistic-Roman periods. A series of scarps obtained at sub-bottom profiles at a water depth of 8 m was considered as evidence for the ancient shoreline. A lowering of the sea level at 8 m is comparable with the archaeological evidences and indicates a local subsidence rate of 3.5 mm/yr. The low sea level stand revealed submerged or exposed, rocky islets offshore the Pharos Light-house which in combination with the very narrow (in relation to the present day) entrance to the Eastern Harbour were complicating the ancient mariners. In addition, the low sea level stand revealed the Ridge A, located submerged off the Eastern Harbour, as a natural breakwater. Therefore, the tobolo of Heptastadion, the island of Pharos and the breakwater (Ridge A) had developed a natural system, almost encircling the Harbour, preventing the entrance of high waves in inshore waters and reducing the coastal erosion. The findings of the present study are consistent with the descriptions of the ancient writers.