dAf 86
RIETH Éric, CARRIERRE-DESBOIS Catherine et Virginie SERNA
L'épave de Port Berteau II (Charente-Maritime)
Un caboteur fluvio-maritime du haut Moyen Âge et son contexte nautique
Discovered in 1973, the Port Berteau wreck lies at a depth of 7 metres in the Charente river below Saintes. Excavations (1992-1997) were carried out with the dual objective of studying both the hull’s remains and its natural environment.Using the traditional techniques of ship archaeology to examine the wreck from the stem to the stern-post has enabled archaeologists to draw an “architectural portrait” of an early 7th century coaster. The 14.30 metre carvel built “frame-first” boat was intended for river navigation and built to carry a cargo of up to ten tonnes. Using what could be called a naval archaeology approach, researchers have analysed the river environment to reconstruct the natural landscape of the period. The Port Berteau II coaster thus provides a reference for carvel construction history in the Ponant, previously attested only in 15th century texts.
Abstract
Abstract
1 Research framework
The Port Berteau II wreck, discovered in 1973, lies at a depth of 7 metres on the bottom of the Charente river. It is located 50 metres downstream from the medieval and modern harbour of Port Berteau, which is on the right bank of the Charente below Saintes (Charente-Maritime). Excavation of the site (1992-1997) marked the final stage of a research project begun in 1971 and dedicated to medieval river transport. The project was concerned not only with boats, but also with changes made to the banks and the Charente’s low-water channel. The principal stages were : excavation of the harbour site (1971-1972) ; prospecting and recording along a 40 kilometre stretch of the river between Port-d’Envaux below Saintes and Dompierre-sur-Charente above (1984-1986) ; excavation of the 11th c. wreck and the river site at Orlac (1987-1988) ; and lastly, excavation of the wreck and river site at Port Berteau II. Located on a part of the Charente which is tidal, the wreck and site at Port Berteau II are part of a sea-river environment which is both different from and complementary to that studied at Orlac, where the context is strictly that of the river.
On the basis of choices made during the study of the Orlac site, the underwater excavation of the Port Berteau II wreck was designed as that of an “open structure” directly related to its river environment. The remains of the hull were to be examined using both traditional methods of ship archaeology in order to determine the vessel’s technical characteristics and newer methods of nautical archaeology so as to reconstruct the main characteristics of the medieval river environment. From the outset, an excavation strategy based upon this dual approach brought together a study of the hull’s remains and, simultaneously, an examination of the site using topography, geo-archaeology, sedimentology and palynology.
2 The river site
In recent times the Charente river has undergone many alterations. The most significant of these was the construction of the Saint Savinien dam, located 17 kilometres downstream from the wreck site, which now lies 7 metres underwater. The normal width of the river is approximately 45 metres. The low-water channel is off-centre and located some ten metres from the left bank which is low and steep. The right bank has a sharp incline leading down onto a gently sloping sedimentary shore. A longitudinal section of the riverbed, studied over a distance of 150 metres, shows a flat relief with no major topographical anomalies. Since it is likely that the depth of the river previous to the building of the Saint Savinien dam was between 1.50 and 2 metres, the riverbanks would have presented a different profile. The left bank, where man-made change is recent, would have resembled a sedimentary shore, whilst the right bank would have been little different, that is to say a gently sloping glacis. The idea that the right bank might have extended as far as the centre of the present day river cannot be ruled out. This hypothetical reconstruction suggests that the old river bed would have been closer to the left bank, where the wreck was found.
Given the proximity of the Port Berteau harbour, research was carried out on the pottery deposit which covered the wreck. Most of the finds, which came from a surface layer of shell-bearing sand, comprise regional pottery identical to that found in excavations of the harbour site. Two pottery groups are of significance in terms of their number and weight. One group is comprised of 13th and 14th century ware, the other of pottery from the 18th century. Most of the medieval pottery would seem to have been brought to the Port Berteau II site by flood waters. It is likely that a great deal of the modern pottery is the result of accidental loss or intentional disposal of defective items in the water.
Another significant dimension of the information gleaned from the river site concerns the process by which the wreck silted up and was covered over. Stratigraphic sections from both inside and outside of the wreck, together with the study of core samples taken by the Centre National de Préhistoire at Périgueux, have brought to light the presence of a lower layer, older than the one in which the wreck lies. The earlier layer contained a piece of driftwood which radiocarbon dating assigns to approximately the year 534 A.D. Also visible were a middle layer resulting from flooding, which may well be related to the boat’s sinking, and an upper layer where the fill of the boat’s broken hull had been cut into. The cut, probably man-made, may reflect an attempt to salvage equipment or the ship’s timbers.
The results of the river site study suggest that the boat had been carried off by a flood at the beginning of the 7th century whilst either wintering or being repaired on the right bank of the Charente close to the harbour. This hypothesis raises the question of whether a repair and wintering point existed before the harbour came to be used for shipping pottery from the workshops in the Saintes area.
3 The wreck
The wreck, lying upside down on the bed of the Charente, is 14.60 metres long and 4.80 metres wide. The rear of the hull is preserved to a height of around 1.70 metres. Dendrochronology measurements carried out on ship-timber samples by the Chrono-Ecology laboratory in Besançon indicate that the oak used came from trees cut down during the winter of 599 A.D. and that the boat was built during the year 600.
The hull, whose pointed ends are formed by a stem and a stern-post, is made up of a dense assemblage of ribs, a series of cross-beams whose protruding ends are slotted into the sides, carvel planking whose joints are caulked with plant tow, a fore and aft deck, and a support for one (or two) side rudders which resembles a cross-beam but has extremities which extend beyond either side of the boat by 1.60 metres and 1.65 metres respectively. The carvel planks are not linked and are fixed to the ribs with wooden pegs and to the stem and stern-post with nails. These building techniques appear to be those used on sea-going ships and are very different from those used on strictly river-going vessels which are known to have existed in the Charente area during the Middle Ages and are generally one piece or assembled dug-outs.
4 The vessel
Architectural reconstruction of the bottom part of the boat shows that it was partly decked, built on a keel, and measured 14.29 metres long at the gunwales and 4.80 metres wide at the main frame. Unloaded displacement, with the hull equipped, was in the order of 6.8 tonnes for a 0.36 metre draught and a 0.90 metre free board. Its load capacity can be estimated at around ten tonnes. Architecturally-speaking, the boat seems to belong to a carvel built “frame first” ship-building tradition in which the cross-timbers have a central role both from a design and a structural point of view.
Given its age, the boat is the oldest known example of this building technique on the Atlantic sea-board. Written evidence had previously dated the development of carvel construction at Ponant to the second half of the 15th century. The Port Berteau wreck will lead to a re-examination of this major phenomenon in the history of medieval naval architecture.
From a functional point of view, the Port Berteau II boat, rigged with a square sail whose surface measures 50 square metres, belongs to the family of coasters suited to short-distance coastal and river navigation. It is likely that this rather small maritime sailing area was also where the boat-yard and the plants used for caulking the hull would have been found. Floral analysis suggests that the plants were part of an environment located along either an estuary or the coast. The region was marked by its lack of access to the open sea until the port of La Rochelle was developed in the middle of the 12th century. In this context, the Port Berteau II coaster possessed the architectural and functional features best suited to local sea and river trade within a “nautical area” bounded on the West by the Ré and Oléron islands, and on the East by the three waterways (the Sèvre-Niortaise, the Charente and the Seudre) which linked the coast to the hinterland.
