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Landscape evolution in the Grand Marais of Limagne (Puy-de-Dôme, France), from the Iron Age to modern times. An archaeological and paleoenvironmental study in a long-lasting perspective

Final Activity Report Summary - GRAND MARAIS (Landscape evolution (...) from the Iron Age to modern times. An archaeological and paleoenvironmental study in a long-lasting perspective)

The principal aim of the GRAND MARAIS project was to define landscape evolution, from the late Iron Age until modern times, of the Grand Marais of Limagne, in Puy-de-Dôme, France, a plain of 150 km2 area that is located east of the town of Clermont-Ferrand. In particular, the essential question of the ‘heritages’ and long-term trends in territorial patterns was considered.

Based on archaeological researches carried on during the last ten years, we could say that, since the end of the Bronze Age, this region was affected by a high density of population in the form of a scattered settlement, which reached its main extent at the beginning of the Roman period, i.e. during the first and second centuries A.D.

The first step of the research consisted of the collection of all available documentary sources, such as cartography (modern and contemporary), aerial photography (panchromatic, colour and infrared) and archaeological data. All data were prepared, i.e. digitised and delocalised, in order to allow for their insertion into a geographic information system (GIS).

Recent geomorphologic researches showed that the plain of Grand Marais of Limagne, whilst generally considered as a wet area on the whole, should more correctly be intended as a sort of a puzzle, in which different zones are distinguished by a different degree of humidity. Therefore, a crucial step of this research consisted in detecting and spatialising wetlands inside Grand Marais. This result was achieved by means of an infrared analysis, in collaboration with the department of mechanical and civil engineering, University of Modena and Reggio, Italy, combined with a regressive analysis, which was conducted on photographic and cartographic representations with particular reference to the 19th century cadastral maps.

I afterwards searched for regular agrarian patterns in modern Grand Marais plain. This part of the analysis was carried out on the cartographic and photographic representations of this plain. In particular, I looked for regular patterns corresponding to Roman units. They were in fact likely to be the result of a planned intervention dating back to Roman times. For instance, this was the case of Roman centuriation, a regular organisation of the countries, generally carried out with the aim of land reclaiming in accordance with a grid having a side of about 710 m, which corresponded to 20 Roman actus. I tested the pertinence of many centurial grids, according to the variations of the Roman feet, in order to verify the possible existence of a centurial system in the Grand Marais plain. Finally, I found the possible pertinence of a grid of 710 m, irregularly attested in almost the entire plain, oriented north-south and east-west and materialised on the ground by roads, canals and boundaries.

The pertinence of this regular agrarian pattern to the Roman period was tested on the basis of data resorting from archaeological excavations, with a particular attention to linear structures connected with territorial organisations, such as roads and ditches for drainage and irrigation purposes. Archaeological data seemed to confirm the existence of a main north-south and east-west orientation, compatible with the territorial pattern that was recognised on cartographic and photographic representations and dated back to Roman times.

In this way, I demonstrated the pertinence of the territorial model called ‘paysage de fondation’ for the Grand Marais plain, which was represented by a landscape regularly planned during Roman times. This model could be opposed to the one called ‘paysage de formation’, in which the territorial pattern would form progressively and independently from any form of regular planning.

From the historical pertinence point of view, the hypothesis of a centurial system (model of ‘paysage de fondation’) organising, at least partially, the Grand Marais plain, was perfectly plausible and coherent with the important transformations after the Roman conquest of this region. The foundation of the town of Augustonemetum, today referred to as Clermont-Fd, and the concomitant reorganisation of the road network around Agrippa’s way at the beginning of the first century A.D. could have been accompanied by a radical reorganisation of the plain.