Étude tracéologique des bois de construction du port romain de Saint-Lupien à Rezé/Ratiatum (Loire-Atlantique)

Résumé Fr En

La conservation des bois présents au sein des caissons nos 9 et 12 du quartier portuaire de Saint-Lupien à Rezé/Ratiatum (Loire-Atlantique) a permis d’identifier une grande diversité de techniques de façonnage et de mise en œuvre de ces matériaux dans le cadre d’un chantier de construction monumental réalisé en contexte fluvial entre la fin du ier s. et le milieu du iie s. apr. J.-C. L’analyse de ces bois a également apporté de précieuses informations sur le potentiel forestier à cette époque et sur les conditions d’approvisionnement en bois d’œuvre d’un grand chantier de construction aux abords de la Loire.

The dendroarchaeological and traceological study of the timber wood preserved in the caissons 9 and 12 of the port quarter of Saint-Lupien in Rezé/Ratiatum (Loire-Atlantique), dated between the end of the 1st c. AD and the mid-2nd c. AD, made it possible to highlight the fact that the building site experienced difficulties in the supply of quality timber. The large master beams of the caissons were cut from timber stemming from trees felled between 88 and 93 AD, in addition to reused beams stemming from a similar caisson, built barely a decade earlier. Most of these timbers were cut from oversized, gnarled oak trees, some of which were sawn. Their anatomical profiles suggest that they were trees from undergrowth or degraded open woodland. The forests that were exploited were not be able to supply the building site with straight-grained, knot-free wood with a diameter perfectly suited to the needs of the carpenters, despite the possibility of transport by the Loire river. As a result, one of the beams revealed the traces of a completely new machine used to cut it to length. The numerous closely spaced semi-circular grooves preserved in the mortises suggest a manual machine with a toothed circular disc 0.48 m in diameter with a very rapid movement, characteristic of a circular saw. This would be the first mention of this type of machine before its diffusion at the end of the 18th c. in Europe. Several stamps were observed on beams and piles, probably indicating orders placed with workshops or timber merchants. The numerous traces on the beams also made it possible to reconstruct most of the techniques used to build the wooden sections of the caissons, i.e. the stitching of the pile and beam assemblies, as well as the marking of the assemblies thanks to the many preserved Roman numeral marks. The preservation of the low beams in a wet environment also offered the possibility of inventorying different types of joints, some of which are quite remarkable, such as the end jointed lumber equipped with a mortise and tenon or the straight crosses in the middle of the wood for the corners of the caissons. Finally, certain clues have made it possible to suggest the steps involved in lifting the wooden structures of the caissons.