04-2021, tome 118, 1, p. 99-146 - C. NICOLAS, Y. PAILLER, P. STEPHAN, J. PIERSON, L. AUBRY, B. LE GALL, B. LE GALL, V. LACOMBE, J. ROLET - La carte et le territoire : la dalle gravée du Bronze ancien de Saint-Bélec (Leuhan, Finistère)

La carte et le territoire : la dalle gravée du Bronze ancien de Saint-Bélec (Leuhan, Finistère) p.99-146

Clément Nicolas, Yvan Pailler, Pierre Stéphan, Julie Pierson, Laurent Aubry, Bernard Le Gall, Vincent Lacombe & Joël Rolet

Résumé : La dalle gravée de Saint-Bélec a été mise au jour par P. du Chatellier en 1900 dans un tumulus de l'âge du Bronze ancien à Leuhan (Finistère). Presque tombée dans l'oubli pendant un siècle, cette dalle ornée a été récemment redécouverte dans les caves du Musée d'archéologie nationale et a pu faire l'objet de plusieurs scans 3D. Cet article présente les résultats de l'analyse morphologique, technologique et chronologique des gravures, qui s'organisent en une composition relativement homogène. L'absence de toute météorisation des gravures suggère que la dalle a été enfouie peu de temps après leur réalisation. La présence de motifs répétés de formes circulaires, quadrangulaires et de cupules, joints par des lignes donne l'allure d'un tracé cartographique à cette composition. Des comparaisons menées avec d'autres représentations similaires tirées de la préhistoire en Europe et ailleurs dans le monde montrent qu'elles sont généralement comprises comme des cartes topographiques en plan, ce que tendent à confirmer les données ethnographiques. Un examen de la surface gravée montre que la topographie de la dalle a été volontairement modifiée pour, semble-t-il, représenter le relief environnant, tandis que plusieurs lignes paraissent figurer le réseau hydrographique. Cette hypothèse est testée et validée par plusieurs analyses statistiques de formes et de réseaux. Plusieurs motifs gravés évoquent diverses structures de l'âge du Bronze ancien (enceinte, système parcellaire, tumulus, route). Enfin, la cartographie vraisemblable d'un tel territoire est mise en perspective avec le contexte socio-historique des tumulus armoricains, qui témoigne d'une forte hiérarchisation sociale et d'un contrôle sans doute étroit de l'économie.

Mots-clés : Art rupestre, planimétrie, analyses spatiales, territorialisation, âge du Bronze, Bretagne.

Abstract: The intricately carved Saint-Bélec slab found in the Leuhan parish (Finistère) was found within an early Bronze Age barrow in 1900 (fig. 1 and 2). A recent re-examination of the Saint-Bélec slab suggests that its sculptured surface and scattered motifs represent the surrounding landscape and a series of contemporary structures now known from archaeological evidence. When discovered, the slab formed the western side of one of the largest stone-cists in the region. It was orientated east-west and measured 3.86 m long, 2.1 m wide, and 1.86 m high (fig. 3). However, at the time of its excavation, the slab was partly broken, presumably in antiquity, with the upper part missing. It was surmounted by several layers of rubble stone (fig. 3, no. 6). Within the grave, was a broken ceramic vessel, now lost but characteristic of early Bronze Age pottery. The study of the slab was conducted using whole slab observations, general and detailed photographs with oblique lighting, and several 3D survey methods (photogrammetry, general and high definition 3D-scanning) to record the surface topography of the slab at different scales and to analyse the morphology, technology, and chronology of the engravings (tabl. 1, fig. 5 and 6). The generation of a 3D-Digital Elevation Map from high definition 3D-scanning and various visualisation techniques was the basis for subsequent interpretation and analysis (fig. 7 and 8). The slab is a grey-blue coloured schist, c. 2.2 m long, 1.53 m wide and 0.16 m thick. Under polarized light, the groundmass appears to be typical of the Douarnenez Phyllade series that form locally the bedrock in the Saint-Bélec area (fig. 4). All the engravings are relatively fresh and show no trace of weathering (fig. 8, no. 1 and 2), although they have suffered biological, chemical and mechanical alterations in recent times (fig. 9). This suggests that the carved slab was not exposed in the open air for long. The motifs cut into the surface are relatively uniform and show simple geometric shapes: i.e. round and oval cup-marks; straight or curved lines; and squares, circles, ovals or curved shapes (fig. 10). Some associations between motifs appear to form recurrent patterns, for example one or more cup-marks included in a closed shape, and cup-marks at line ends or intersections. One of the peculiarities of the Saint-Bélec slab is its sculptured surface. A triangular hollow has been carved out from the centre to the left-hand end. Its upper and lower edges have been shaped by two deep-pecked bas-reliefs (B1, B2/B3), the lower one having been split and cemented together in recent times (fig. 11). In between, the surface was variously weathered or freshly flaked by pecking related to superimposed motifs, suggesting that the triangular hollow probably took advantage of a pre-existing depression in the surface of the slab (fig. 8, no. 1). While there are relatively few blank areas on the decorated surface, there is very little overlap of the motifs, except at their ends. Therefore, it appears that the successive phases in creating the panel did not significantly change the overall composition but were rather added in a planned way (tabl. 2 and fig. 11). The main issue about the dating of the Saint-Bélec slab is its probable re-use. Stylistically, the motifs are quite different from those found in the regional Neolithic traditions of ???megalithic??? art. This is supported by the freshness of the engravings which implies a relatively short time-span between their creation and the subsequent burial of the slab. The most spectacular characteristic of the Saint-Bélec slab is its map-like pattern that consists of a homogeneous composition of repeated motifs joined by a series of lines. Comparisons with other similar representations from prehistoric times in Europe and elsewhere in the world show that they are commonly regarded as plan topographical maps (fig. 12 and 13); a hypothesis which is further supported as well by ethnographic data (fig. 14 to 16). A key point is that the engravers seem to have modified the original surface relief of the slab to create the desired 3D-form that compares to the topography of the surrounding landscape, the upper Odet River valley, overlooked by the Saint-Bélec barrow (fig. 17, no. 1 and 2). Furthermore, a series of lines appear to figure a more extended river network (fig. 17, no. 3 and 4). To test this hypothesis, we have led several network and shape analyses that confirm a good correspondence between the carvings and the topography (fig. 18), with similar results to ethnographic solicited maps (fig. 19). Such correlations give the opportunity to georeferenced the Saint-Bélec slab and get an idea of the possible scale of the space represented: an area c. 30 km long and 21 km wide (fig. 17, no. 5). Furthermore, the carved motifs might have depicted early Bronze Age settlements, barrows, field systems, and tracks (fig. 20, no. 1 and 2, 21 and 22). The early Bronze Age in Brittany is well known for its princely burials (fig. 23) which are regularly distributed in western Brittany and are assumed to reflect the centres of established territories that can be modelled using Thiessen Polygons. Although no such burial is known in the area, the central motif on the Saint-Bélec slab could be interpreted as a central place of an early Bronze Age territory, extending over an area of 545 to 843 sq. km (fig. 20, no. 3 and 4). One outstanding question about the Saint-Bélec slab is why it was made? One possibility is that such a territorial depiction was a material and symbolic act enforcing. Set alongside the contemporary development of field systems in Brittany making the slab perhaps suggests the appearance of a new form of land tenure, while the distribution of elite graves is closely linked to soil fertility. Against this background, we can hypothesize that the Saint-Bélec slab was used as a cadastral plan for managing the territory and controlling land.

Keywords: Rock art, planimetry, spatial analyses, territorialisation, Bronze Age, Brittany.