Biographie d’un monument mégalithique du Néolithique moyen sur la côte sauvage de Quiberon dans le Morbihan

International audienceSeveral preventive archaeology operations carried out between 2016 and 2019, in the village of Manémeur on the wild coast of Quiberon, have brought to light the last remains of a Neolithic megalithic complex whose advanced state of degradation has caused the disappearance of almost the entire elevation. This monument was originally described as consisting of three dolmens included in a single cairn, arranged on the same line running from north to south. Before our intervention, it had already been the subject of several investigations at the end of the 19th century and in the 1930s.In spite of this, the exhaustive excavation has revealed the modes and phases of construction of this complex monument, built in several stages.It is a cairn including two dolmens with quadrangular chambers and fairly long passages. They are parallel and open to the southeast. The partial plans of the sepulchral spaces could be reconstructed thanks to the presence of either the remains of broken granite standing stones, or the pits where the torn off elements were wedged in place, or, in dolmen 2, the intact orthostats. The circulation levels in these spaces were identified thanks to the paving of the floors, megalithic for that of the chamber of dolmen 1. The excavation revealed the relative chronology of the main construction phases of dolmen 1. The two parts of the corridor have sufficiently different characteristics to suppose that they were built in two phases, with a first northern portion extended by a southern portion, and are part of successive architectural projects. The chamber of dolmen 2 rests against the facing of the chamber of dolmen 1, implying that the latter was built earlier. The excavation was a unique opportunity on the Morbihan coast to study the basic structures and foundations of a monument of this type, revealing the internal partitions of the cairn and the preparation levels intended to receive the paving of the internal spaces.The cairn, as well as the facings and orthostats of the monument, is made up almost exclusively of granitic elements, even if a few blocks of quartz or pegmatite are occasionally present. If most of them have less sharp edges that indicate an extraction, the construction of the external facing is clearly distinguished from the rest by the placement of blunt blocks with rounded shapes attesting to a collection on the foreshore.The substratum underneath the monument, exposed at the end of the excavation, revealed traces of extraction of large slabs prior to the erection of the monument. The extraction was facilitated by the flaky texture of the granite and a network of diaclases that cut the massif into parallelepipedic blocks.At the same time, it has allowed a regularization of the terrain, inscribed on an eminence linked to a granitic rise. The micromorphological study showed that the soil covering the substratum had largely been reworked, most likely scraped to allow extraction and then respread before construction. Some large quartz impactors as well as several bevelled pieces are likely to have participated in the removal of the granite slabs.The associated archaeological material, which is quite abundant, has made it possible to attribute dolmen 1 to the end of the Middle Neolithic II, which is confirmed by radiocarbon dating. Dolmen 2, less rich, yielded more mixed material, most of which points to an attribution to the beginning of the Late Neolithic. Exclusively discovered under the floor levels of the monument, these ceramic and lithic materials have a very uneven spatial distribution that does not seem fortuitous and is probably the result of staging. Similarly, environmental studies have indeed revealed the presence of plantain, Plantago lanceolata for carpology and Plantago coronopus for palynology, whose very high concentrations argue for an anthropic spreading. These remains and their arrangement inside and outside the funerary space thus testify to deposits associated with the foundation of the monument, which constitute practices that are rarely discussed because they are too rarely brought to light.The Manémeur site is part of a vast group of monuments of the same type (passage graves enclosed in a terminal cairn) identified in the vicinity and more widely on the Morbihan coast. Many of them belong to the Middle Neolithic or the late Neolithic. Although some of them group up to four passage dolmens in the same cairn, the relative chronologies are not always clearly established and the internal structures of the cairns have not been explored much.The excavation carried out here has brought new light and new knowledge to this ensemble, showing at the same time all the informative potential of the exhaustive study of such monuments, even when they have been largely destroyed.Plusieurs opérations d'archéologie préventive réalisées entre 2016 et 2019, dans le village du Manémeur sur la côte Sauvage de Quiberon, ont conduit à la (re)découverte des derniers vestiges d'un ensemble mégalithique néolithique dont l'état de dégradation très avancé a fait disparaître la quasi-totalité de l'élévation. Malgré cela, la fouille a constitué une opportunité unique sur le littoral morbihannais d'étudier les structures de base et les fondations d'un monument de ce type, mettant en évidence des cloisonnements internes au cairn et des niveaux de préparation destinés à recevoir les dallages des espaces internes.Il s'agit d'un cairn incluant deux dolmens à chambres quadrangulaires et à couloirs assez longs, parallèles et s'ouvrant au sud-est. Les plans partiels des espaces sépulcraux ont pu être restitués et les niveaux de circulation identifiés grâce aux dallages des sols, mégalithique pour celui de la chambre du dolmen 1. La chambre du dolmen 2 prend appui contre le parement de la chambre du dolmen 1, impliquant l'antériorité de ce dernier.Le substrat sous-jacent au monument mis à nu en fin de fouille a révélé des traces d'extraction de grandes dalles préalablement à l'érection de ce dernier. L'étude micromorphologique a montré que les terres qui recouvraient le substrat avaient été en grande partie remaniées, très probablement raclées pour permettre l'extraction puis réétalées avant la construction.Le mobilier archéologique associé, assez abondant, a permis d'attribuer le dolmen 1 à la fin du Néolithique moyen II, ce que confirment les datations radiocarbone. Le dolmen 2, moins riche, a livré un mobilier plus mélangé, dont l'essentiel oriente vers une attribution au début du Néolithique récent. Exclusivement découverts sous les niveaux de sol du monument, ces mobiliers céramique et lithique ont une répartition spatiale très inégale qui ne semble pas fortuite et résulte très probablement d'une mise en scène. De la même façon, les études environnementales ont révélé la présence de plantain, Plantago lanceolata pour la carpologie et Plantago coronopus pour la palynologie, dont les très fortes concentrations plaident pour un épandage anthropique. Ces vestiges et leur disposition dans et en dehors de l'espace funéraire témoignent de dépôts associés à la fondation du monument