Roman Ports in the Mediterranean: Geomorphology, Environment and Resilience

Abstract

Classical ports in the Mediterranean Sea existed not only in a social, economic and technical contexts but also in a geomorphological context. This geomorphological context, which includes both the harbour landform and the catchment (if any) is a function of the geomorphology of coasts and catchments (including neotectonics) and marine factors (bathymetry, low amplitude tides, surges, tsunamis etc.). A simple geomorphological analysis of the major Roman 50 ports of the Mediterranean shows that they are dominated by river mouth (42%) and lagoonal/deltaic settings (16%) but also included rocky bays/promontories and totally artificial basins (14%). All types of Roman ports had siltation problems, as nearly all ports do, but this is even more pronounced for river-mouth ports all of which suffered, partly due to low tidal amplitudes and supressed estuarine energy regimes. Many adaptations can be illustrated including construction materials, mole design, dredging, and not infrequently, changing port location. The resilience of river-mouth ports was closely connected to river catchment dynamics of erosion and sediment transport as well as socio-political factors. The generally short, and relatively steep gradients, of most rivers entering the Mediterranean (with obvious exceptions) limited the storage space for fine sediment, and resulted in high rates of estuarine and deltaic plain sedimentation. A recent analysis of pan-Mediterranean erosion by Walsh et al. (2019) has shown that although erosion/sedimentation rates varied catchment to catchment, there was a general increase over the early Roman Period followed by a decline, and then an increase again in the Medieval Period, although some regions, e.g. S France are out of phase with this pattern. Optically-stimulated luminescence (OSL) dating of sediments in the Tiber catchment shows a pulse of sediment deposition in the late Roman-early Post Roman period and again later in the Renaissance (c. 1500-1700 AD) caused by a combination of intensive cultivation and climate, including the Little Ice Age. This paper concludes that the history of Roman ports cannot be de-coupled from their sediment-catchments, either coastal cells and/or fluvial catchments, as both placed heavy burdens on the sustainability of ports but to different degrees. Along with technological change and the geopolitics of trade these geomorphic factors played a role in the spatially differential resilience of Mediterranean ports during and after the Roman period.