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RESEARCH PRODUCT

L’usage des trachytes de la chaîne des Puys depuis deux millénaires

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The very recent work carried out within the framework of a Collective Research Project (PCR-Trachytes) supported by the Auvergne-Rhône-Alpes Regional Directorate of Cultural Affairs has completely renewed our knowledge of the use of trachytic lavas from the chaîne des Puys over the last two millennia. A complete petrographic identity sheet has been established for each of these trachytes. This database showed that each trachytic volcano was made up of a different lava from those of its neighbours, except for Cliersou and Aumône which have the same lava. Moreover, for the Puy de Dôme and the Cratère Kilian, it was shown that they were each made up of two different lavas. Thus, the fine characterisation of the materials used in buildings, tombs or sculptures elsewhere in the region now makes it possible to trace them back to the original volcano.During Antiquity, the Temple of Mercury at the top of the Puy de Dôme, the buildings of the Ceyssat Pass agglomeration located on the Agrippa road and the Tourette d'Enval sanctuary were built with one of the Cratère Kilian's trachytes from an important quarrying centre opened for this purpose. Several cinerary chests or statues made from the same material have also been found within a radius of about fifty kilometres around Augustonemetum (Clermont-Ferrand).During the High Middle Ages, the practice of burial in stone sarcophagi became widespread. Around the Puys chain and up to a hundred kilometres away, the archaeological excavations of necropolises from this period has revealed hundreds of sarcophagi carved in trachyte. In addition to the ancient quarry of the Kilian Crater, numerous underground exploitations, some of which were discovered in the course of this work, were used for this purpose. They concern the volcanoes Grand Sarcoui, Cliersou-Aumône and the upper part of the Cratère Kilian.The construction of important religious buildings in the region during the Romanesque period also made use of trachytes from the chaîne des Puys. In addition to the occasional use of sarcophagus fragments, building stones, architectural decorations and sculptures were made from lava from the Dôme, Chopine, Cliersou-Aumône and Sarcoui puys. The corresponding quarries remain unknown.In modern times, attempts were made to diversify the use of this rock. The only one that experienced some industrial development was the use of the ashes of the Grand Sarcoui to make glass. For the rest, all the trachytes of the chaîne des Puys have been used opportunistically in traditional civil construction (framing of openings, chaining). A specific use concerns village bakehouse, more particularly the sole (floor) and the voûte (vault).Thanks to this work, the trachytes of the chaîne des Puys can now be used by archaeologists and historians as indicators of ancient economic circuits and craft practices.