Paleoenvironmental reconstruction of the ancient harbors of King Louis IX (Aigues-Mortes, Rhone Delta, France)

This article presents the paleoenvironmental, archaeological and geophysical results obtained in 2015 at the medieval port city Aigues-Mortes, founded by Louis IX in 1240. The fortified city is now located five kilometers from the sea, in an environment different than the medieval landscape. Our team studied the medieval port of Aigues-Mortes, its location, its geographical limits and its links to the city. Our analyses also concentrated on environmental processes and the factors responsible for changes in these processes. Two zones, one dry and one submerged (the port basin), were identified. The dry zone consists of medieval backfill intended to raise ground that was too wet. This zone starts at the foot of the wall and measures almost 20 m wide. Part of the fill material consists of large stones deposited by humans in order to build a pier or slipway, or possibly intended for ballasting ships. The port basin was shallow near the wall and clogged up rapidly. This hypersedimentation required dredging works and the construction of a ship canal. The decline of the port was swift, and can be explained by poor hydraulic works and rapid environmental changes (early stages of the Little Ice Age). The adaptation strategies of the past societies were not sufficiently effective or durable. The cost of the works was too high in a period characterized by armed conflicts, deadly plagues and the emergence of rival ports.