Geoarchaeology of Portus Mareoticus: Ancient Alexandria's lake harbour (Nile Delta, Egypt)

International audienceAncient Alexandria possessed not only an important maritime front but also a long lake waterfront on its southern side. This dual waterfront was praised by the ancient geographer Strabo in the first century BCE, because its geomorphological configuration opened Alexandria to Mediterranean trade, and also the Nile delta and Egypt. While the city's maritime palaeogeography has been widely described and studied, Alexandria's lacustrine waterfront has largely been neglected and little is known about its palaeo-geography and archaeology. Here we report the chronostratigraphy of the southern edge of the modern city. Bio-sedimentological analyses of sediment archives allow us to reconstruct the evolution of the depositional environments and palaeogeographies for parts of ancient Alexandria's lacustrine waterfront. The chronological framework spans the last 2000 years. By marrying our data with ancient maps and historical sources, we propose a location for Portus Mareoticus. The lake's geomorphology suggests the presence of three ancient jetties, perpendicular to the shoreline and several hundreds meters long. The occupation of the investigated area began at the end of the first century BCE, linked to Roman domination and probably ended during late Roman times. The waterfront was then disconnected from the city during the 9th century CE, due to the desiccation of Maryut Lake, concomitant with the drying-up of the Canopic branch. Alexandria canal subsequently became the sole waterway linking the city to the Nile. The most western part of the canal, which extended freshwater supply and fluvial navigation down to the western marine harbour of Alexandria, was completed in the 16th century, probably in relation to the development of the marine harbours at the beginning of the Ottoman period. Our research sheds new light on the topography of ancient Alexandria