Climate, hydrology, land use, and environmental degradation in the lower Rhone Valley during the Roman period

This paper's aims are three: firstly, to demonstrate the importance of a long-term perspective on socio-environmental dynamics; secondly, to show the relevance of archaeological data in constructing such a long-term history of such dynamics; thirdly, to illustrate with a case study how one may identify the component processes of environmental change from archaeological materials. Taking the Roman occupation of the middle and lower Rhone Valley as a point of departure, the paper identifies some of the processes of regional environmental change. Firstly, it demonstrates the existence of a regional phase of climate degradation during the 2nd century ad. It is in all probability of anthropogenic origin. This degradation seems to have been caused by widespread deforestation in preparation for intensive cultivation of cereals, wine and olives for export to other parts of the Roman Empire. Next, it isolates the principal interactions occurring between relief, soils, and water on the one hand, and the societal dynamics on the other. The location of each settlement is considered representative of an environmental choice, made by its founders at the time the settlement is initiated. These environmental choices, in turn, reflect the perception of the landscape and its resources by the settlers. The principal indicators at our disposal for this study are the relief, soil, and hydrological maps. They are used as a basis for the calculation of the altitude, slope, orientation, annual solar radiation, exposure to the prevailing winds, and fertility of the soil of all sites and their environment. Subsequently, preferences are calculated statistically based on the 1000-odd settlements concerned. The third part of the paper concerns the evolution of the sites. It turns out that the earlier ones are the most successful, in part because they occupied the best locations, but also because they structured the landscape and the territory to their advantage, determined the road network, and were the first to lay hands on localized resources. Eighty percent of the total number of sites is abandoned in less than 200 years. The reasons for that abandonment are not to be sought in any kind of environmental degradation, as the proportion of abandoned sites is about the same in all landscapes. Rather, they seem to have to do with a reorganization of the settlement pattern after some 100 years of increasingly intensive agro-industry. This reorganization is triggered by a combination of economic and political events that come close to destabilizing the Empire. Settlement size and accessibility are the main determinants of survival. The exact nature of the events leading up to this re-structuration differs from region to region. In the case of the Tricastin, the Emperor undertook a vast land reclamation project in the first century bc. He used it to retire soldiers from the many legions that were active around the time of the birth of Christ. However, the peace of the early decades of the first century ad abruptly reduced the number of soldiers to be retired. Hence, the orthogonal, Roman drainage system could no longer be maintained sufficiently well, to ensure that it functioned correctly. As a result, the surface available for cultivation, and the yield per hectare, fell drastically, and many farms were deserted.