Excavations at Prisse-la-Charrière 2002

Excavations at Prissé-la-Charrière in 2002 took place over a period of 8 weeks in July and August with a team of between 30 and 50 personnel, consisting mostly of British and French University students. Funding for the season was provided by the British Academy, the McDonald Institute for Archaeological Research, the Conseil Général des Deux-Sèvres and the Ministère de la Culture. The project was directed by Dr Chris Scarre (McDonald Institute, University of Cambridge), Dr Roger Joussaume (CNRS, Paris) and Dr Luc Laporte (CNRS, Rennes).

Fieldwork in 2002 concentrated on two separate sectors of the 100-metre long mound:

A. The western terminal

It was at the western terminal of the monument that the clearest sequence of structures has been revealed. The key element is a 23-metre long primary-phase monument with encircling rock-cut that was later incorporated within and buried by the 100-metre mound.

Rotunda grave

At the heart of this primary monument was a small megalithic chamber within a circular dry-stone rotunda. The chamber consisted of five modest-sized limestone orthostats, two to each side, the fifth forming the back-stone of the chamber. An entrance gap through the thickness of the rotunda gave access to the chamber from the east. At one stage this entrance had been closed by a thin vertical limestone slab that served as a moveable door, resting against the ends of the orthostats, but excavations in 2002 indicated that this was not the original arrangement.

In 2002 removal of the blocking in front of this vertical limestone slab revealed a socket cut into the bedrock. This is probably to be interpreted as the seating for a further orthostat (or possibly more than one) that originally closed this side of the megalithic chamber but were subsequently removed when the moveable door-slab was installed. Thus the megalithic chamber may originally have been entirely closed and have consisted of six (rather than five) orthostats, though both the form and material of the roofing remain uncertain.

The outer face of the rotunda was completely exposed along the whole of its periphery, and was shown to consist of a series of short lengths each built in a different manner. The phasing of the work appears to have proceeded from the south-east corner in a clockwise direction. At this south-eastern corner there was a straight length of rotunda façade over a metre long, that ended at a sharp angle. This may represent the remains of an initial rectilinear or quadrangular structure which was subsequently truncated at its eastern end. Thus the façade of the rotunda revealed at least one phase of modification; the megalithic chamber that it encloses had clearly been modified twice (from closed chamber to moveable limestone door; the latter subsequently broken to gain new access); and the entrance arrangements had also been remodelled – as shown by the contrast between the smooth oblique wall-face on the northern side of the entrance contrasting with the dog-leg form of the southern side.

Directly in front of the chamber entrance, cut into the bedrock, a second pit was discovered and excavated (the first having been excavated in 2001). This contained packing stones surrounding the ghost of a circular timber upright. It was noted that this post-hole and the first were in line with the axis of the megalithic chamber, which is oriented slightly obliquely with respect to the main axis of the long mound. This observation leads us to suggest that post-holes and chamber formed an initial module within the constructional sequence. What is difficult to determine is the original form and phasing of the dry-stone rotunda. We may surmise that it was originally closed on the eastern side by the missing sixth orthostat, and the dog-leg in the entrance (southern side) suggests that the dry-stone surround originally continued round the back of this stone. The oblique walling (northern side) represents a re-working following removal of the orthostat and (perhaps) its replacement by the moveable slabs. The relationship of these changes to the outer facing of the rotunda is very difficult to ascertain. The short length of straight façade at the south-east corner suggests an initial rectilinear structure that was subsequently truncated and remodelled. The precise sequence, however, remains open to question.

Western quarry ditch

The quarry ditch that surrounds the primary phase monument had been extensively explored in previous years, notably on the northern side. In 2001, a narrow sondage across the western quarry ditch had revealed a crouched burial on the ditch floor, in line with the long axis of the primary mound. In 2002, the quarry ditch was excavated down to bedrock across the full width of the western terminal. This revealed that the ditch became shallower towards the north-western corner and may have made an irregular join with the probably deeper northern quarry ditch. The more extensive excavation allowed the stratigraphic context of the crouched burial appeared to be more clearly determined. It had been placed within a D-shaped deepening within the ditch floor which extended across entire width of the ditch; furthermore, on one side the body had been ‘sheltered’ by a vertical slab. This, however, did not rest on the ditch floor but in the primary silts. There was no accompanying artefactual material. An attempt to date the skeleton in 2001 failed owing to absence of sufficient collagen, but another attempt with a larger sample will be made in 2003.

A second skeleton discovered at a high level in the ditch fill in 2001, almost directly above the crouched burial on the ditch floor. This higher skeleton has now been radiocarbon-dated to the 14th century AD.

In 2002, a third burial in crouched position was discovered at the south-western angle of the quarry ditch, close to the surface. Its date remains to be established.

Primary mound: eastern part

Another objective of the 2002 season was to complete the investigation of the primary mound to the east of the rotunda, in order to comprehend its form and internal composition. This was achieved by the by the cutting of a series of sections by hand and machine in the body of the mound.

A complete transverse section was cut through this part of the mound by hand. It revealed the asymmetrical nature of the primary mound, at least in its preserved form. On the southern flank, beneath the overburden of phase II material, the surface of the primary mound was capped by a series of flat limestone slabs laid overlapping each other in the manner of a crudely built tiles roof. On the northern flank, there was no surviving trace of any such capping, though it was not possible to determine whether
a) the mound as constructed had only had this capping on its southern flank, or
b) the northern flank had suffered greater degree of erosion and the traces of
this capping had been destroyed.
In favour of the latter argument is the observation that the northern kerb of the first-phase monument had survived only as a basal course of stones, while the southern kerb was preserved in places to a height of 1 metre.

A second transverse machine cut and a longitudinal section along the axis of the primary mound threw further light on its internal stratigraphy. Viewed longitudinally, at the base of the mound were two dumps of material on the long axis; a third had already been documented a little further to the west, and there was space for one more to the east in the unexcavated portion of the primary mound. These dumps were characterised by being composed of or capped by thick layers of red clay, that had probably been stripped from the surface of the bedrock. Thinner layers had been found in the upper part of the primary mound, and horizontal excavation revealed that these corresponded to near-continuous spreads of red clay. The upper clay layers may have marked breaks in the process of construction. The thick clay layers covering dumps along the long axis at the base of the mound, however, must represent the initial stage of its building. In transverse section, it was clear that these initial dumps did not truly lie on the long axis but were significantly displaced towards the north. Careful study of the documentation will allow a 3-dimensional model of these early structures to be prepared.

This further exposure of the first-phase mound led to the recognition that the kerb that fronted it was double-skinned on the northern and eastern sides, but only single on the south. Nothing certain is known of the primary kerb on the western side, where the basal layer of kerb stones had been disturbed by erosion and what survives may correspond rather to the western end of the phase II than of the phase I monument.

B. Passage graves within the Phase II mound

The intact passage grave

Excavation in the central sector of the enlarged long mound concentrated on the new passage grave that had been located in 2001. This stood within a circular dry-stone cairn some 10 metres in diameter.

In the course of the 2001 excavations the southern face of this cairn was exposed along with the later walls that had been built up against it. These later walls belonged to the cell-like structure of the second phase mound, and were for the most part relatively informal structures only a few courses in height that defined small cells up to 2 metres across. Where these walls connected with the circular face of the passage grave cairn it could be seen in all cases that they butted up against it and hence were later constructions. On the south-western side, where more recent quarrying had largely destroyed the prehistoric structures, the excavation of the outer face of the cairn was carried down to bedrock. This revealed that the cairn was constructed on the thin red soil which is the old ground surface above the bedrock. These indications demonstrate that the cairn was the primary structure in this location, a) built on bedrock and b) older than the mound II cell-walls which are consistently built up against it. Hence it must originally have been free-standing and is not part of the phase II monument but belongs to an earlier phase.

Passage and chamber

The passage of this passage grave opens on the northern side and is oriented obliquely with respect to the long axis of the phase II mound. The passage consists of two discrete sections:

a) the outermost 2.4 metres lead through the outer and inner kerb of the phase II long mound, up to the edge of the circular cairn. The side walls of this outer section abut the face of the circular cairn, showing that this part of the passage is a later addition. This part of the passage was excavated down to bedrock, and was closed at its outer end by a blocking wall on the line of the outer kerb of the phase II mound;

b) the inner 3.5 metres of the passage have side-walls forming a continuous angle with the outer facing of the circular cairn, showing that this part of the passage is an integral feature of the early passage grave. The external curve of the circular cairn was continued by a well-built blocking wall across the end of the original passage. This inner blocking wall survived to a height of only 0.75 metres; behind it at this height, the lower part of the passage infill was covered by a layer of slabs, forming a rough paving. Though certainty is impossible, these appearances suggest that at some secondary stage, access to the chamber had been restored by lowering an earlier blocking wall and removing some of the earlier passage fill so as to create a new and very restricted gallery with its floor at approximately half was up the original passage fill. On this raised surface, bones of a child burial were found along with sherds of Neolithic pottery. Excavation in 2002 was halted at this level.

c) the innermost part of the passage, adjacent to the chamber, was not explored in 2002. Excavation on the surface of the cairn, however, exposed more of the passage capstones that had been discovered in 2001. These are of friable local limestone, and it was clear that what had originally been only one or two large slabs had fractured into four smaller fragments. The contrast with the material of the chamber capstone – a large block of an entirely different limestone, of non-local origin – is particularly striking.

No excavation was attempted in the chamber in 2002, and serious technical difficulties will need to be resolved before that exploration can begin. By good fortune, however, the gap between the chamber capstone and the last of the passage capstones proved to be sufficiently wide to enable a digital camera to be inserted and a number of photographs to be taken of the interior. These reveal that the chamber is indeed largely intact, although a part of the western wall has collapsed onto the burial deposit. It has not been entered since the Neolithic.

The chamber is rectangular in plan, some 1.6 x 1.3 metres, and entirely of dry-stone construction, without orthostats. The chamber walls (especially the well-preserved eastern wall) are inwardly corbelled in their upper part; an interesting technical feature that demonstrates that inwardly corbelled dry-stone chambers may nonetheless be roofed by a capstone. The visible part of the burial deposit has a scatter of human bones (including long bones and skulls) with, in the south-east corner, a cylindrical vase-support with triangular perforations or ‘fenêtres’ in its sides. Such vase-supports are characteristic of Middle Neolithic II (cf. Chasséen) assemblages. The thickness of the burial deposit is difficult to estimate, but calculations indicate that its surface lies some tens of centimetres above the level of the bedrock.

The capstone of the chamber has already been mentioned: a large block some 0.30-0.35 metres thick, the upper surface of which has as yet been only partially exposed. It is of a very rough texture and appears to be an ‘aigrain’ or ‘Bathonien à silex’ similar to the capstones of the monuments at Bougon, There, as here, this rough-textured limestone was restricted to the capstones, presumably on account of its engineering properties, whereas finer and more easily worked limestone was employed in the chamber walls.

Additional work on the ruined passage grave

The new chamber is the second passage grave to be discovered within the central section of the Prissé long mound. The first passage grave, a few metres to the west, was a classic dolmen angoumoisin but had been heavily damaged by earlier stone-robbing. Only one of the eight original chamber orthostats had survived. On the southern side where later quarrying had removed or disturbed almost all of the original mound material, the passage grave had been edged by a well-built half-circle of walling, which at first suggested a separate circular cairn similar to that discovered around the new passage grave. Attempts to trace this curved façade around the northern part of the dolmen angoumoisin were unsuccessful, however, leaving the function and visibility of this half-circle in question. Careful cleaning and observation in 2002 suggested that on the west the half-circle had been bonded into a length of east-west walling on the long axis of the long mound. The relationship of the curved wall to the surrounding structures of the long mound needs to be explored on the intact eastern side, however, for the structural sequence to be confirmed. At present, it appears that this western (damaged) passage grave was built as an integral feature of the phase II long mound; whereas the intact, recently discovered eastern passage grave (described above) stood initially on its own within a circular cairn.

The eastern terminal

A major undertaking of the 2002 season was the removal of the protective plastic covering from the eastern end of the mound exposing the structures that had been excavated at the outset of the project. These were cleaned and rephotographed, notably in a series taken by balloon. The results are visually spectacular but will also be of considerable assistance in interpreting the monument.

Radiocarbon dates (see Annex)

Through the good offices of the NERC-funded AMS dating programme at the Oxford University Radiocarbon Accelerator Unit in the Research Laboratory for Archaeology and the History of Art, a series of 12 radiocarbon determinations is now available for the Prissé-la-Charrière long mound. All save OxA-11213 are on human skeletal material. Setting aside two later burials (Gallo-Roman: OxA-10142: and medieval: OxA-11215), these cluster in the interval 4400-4150 BC; the only exceptions being those dates for burials in the ruined passage grave which appear to fall outside this time-bracket by a century or more and may relate to successive inhumations within that chamber. What the remaining dates conspicuously fail to demonstrate is a significant lapse of time between the two main phases at Prissé: the rotunda and ‘short’ long mound (with encircling rock-cut ditch) of the primary phase (OxA-10248 &10249; OxA-11213); and the 100-metre long mound with ruined passage grave of the second phase (OxA-10204, 10205, 10246, 10247 & 10258; OxA-11214 & 11216). Further C14 samples will be submitted in order to confirm these results.

Programme for 2003

The two principal operations scheduled for 2003 are:

1) excavation of the intact passage grave: this presents serious technical difficulties but is an urgent priority if unauthorised illicit entry is to be forestalled

2) re-survey of the monument, and visualisation studies: this work was originally scheduled for 2002 but was postponed pending recruitment of a suitably qualified specialist and the exposure and cleaning of the areas excavated and covered over during the early stages of the project.

Annex: Prissé-la-Charrière C14 dates

First series 2001

Primary monument: megalithic grave within ‘rotunda’

Phase II long mound: ruined passage grave

Single grave on crest of mound (west)

New series 2002

Primary monument (antler on ditch floor)

Ruined passage grave (phalanges in orthostat socket)

Burial on crest of mound (central section)

Burial in upper fill of primary ditch (western terminal)