Hearth structures are probably one of the first expressions of space-specific skills. Building a fireplace is a sign of permanence. Such structures are used repeatedly and can survive beyond the limits of the seasonal occupation. As Gamble (1999) has stressed, they provide a focus of performance and social life. Identifying variations in hearth structures over time is therefore fundamental for understanding the evolution of human social life. Well-built hearths are known from the Middle Palaeolithic. However, they are confined to stone constructions, or well delimited-accumulations of burnt remains. A noticeable change in the manner of using fireplaces is evident in the Upper Palaeolithic. In the Gravettian of Dolni Vestovice fireplaces were used for transforming materials. They have the form of domed and banked clay kilns and they were used for the firing of clay figurines.
Figure 1 – Klissoura Cave 1
The study of the technology of Dolni Vestonice shows an advanced mastering of the raw material possibilities, but unfortunately very little of the hearth structures survived. There is thus little information about the earlier technological steps involved in forming clay kilns and firing clay figurines. The supposed gap between stone constructions or simple delineated hearths of the middle Palaeolithic and the walled clay kilns of the Gravettian may be bridged by the hearth structures in the Klissoura cave 1 (southern Greece).
Figure 2 – Plan view of Klissoura cave showing the excavation grid
Klissoura cave 1 is a complex of a rockshelter and a small collapsed karstic cave located
in a gorge at the northern edge of the Argive Plain in north-western Peloponnese (Figures 1 and 2). Klissoura preserves a long cultural sequence spanning the periods between the Middle Palaeolithic and the Mesolithic; part of the sequence is presented in Figure 3. The Middle Palaeolithic layers (layer VI and below) are overlain by an early Upper Palaeolithic industry characterised by arched backed blades (layer V). Above this lies the first well-dated sequence of Aurignacian occupation in Greece. The Aurignacian layers (IV, all of III, 7, and 6a) have a combined thickness of about 1m and are characterised by steep, carinated and nosed end-scrapers from which bladelets were removed. Special cores for bladelets also occur. A higher frequency of blades and bladelets is observed in the lower part of the sequence. Several bone points and perforated marine shells were also found. Epigravettian layers (layers II) of 0.5m maximum thickness cover the lower sequence through an unconformity and a Mesolithic sequence (layers 3-6) is found locally.
Figure 3 – Stratigraphic section of part of the northern wall (see figure 2). Clay hearth structures are shown in black and interstratified ash remains in gray. Spiral forms indicate the presence of large amounts of snails. Layers 1 and 2 contain mixtures of classical and Bronze age finds, 6 Mesolithic, III c and IIIe upper Aurignacian, IIIf and IV middle and lower Aurignacian, VII and below are Middle Palaeolithic. Note that some of the layers mentioned in the text do not appear on this profile
The lower and middle Aurignacian sequence (layers IV, IIIb, IIIc, IIIe, IIIg, 7 and 7a) in Klissoura cave 1 contained remains of about 90 well-preserved hearths. Some of them just consist of a sequential accumulation of burnt remains. However, 54 hearths have basin-like, clay-lined structures. In addition, the excavations have revealed a well-preserved clay hearth structure with pronounced thickened rims and another 17 similar remains in the uppermost Aurignacian layers of the site (layers III, III’ and III’’, implying a long tradition of producing such structures.
Clay hearth structures were not identified in the Middle Palaeolithic layers, or the layers above the Aurignacian sequence. There were hearths in the Middle Palaeolithic sequence, but these consist of undisturbed sequences of superimposed thin white ash and grey and black charcoal-rich layers. The Epigravettian and Mesolithic layers are characterised by the presence of mostly dispersed burnt remains, but a few thick flat in situ accumulations of ash were also identified, particularly in the Mesolithic layers.
Three radiocarbon dates on organic fractions that have been obtained from the lowermost Aurignacian structures of Klissoura are statistically indistinguishable: Gd-10562 32 400±600, Gd-7892 34 700±1600, Gd-7893 31,400±1000. In the context of this work a new AMS date on charcoal from another hearth structure from the lower part of the Aurignacian layers was obtained. The date, GdA-228 31 150±480, fits very well with the previous three conventional radiocarbon dates. The uppermost Aurignacian layers in Klissoura cave were radiocarbon dated using mollusc shells. After correction for reservoir effect (i.e. 1300 years) the age ranges from c. 26 000 to 22 550 BP. However, other values of reservoir effect for these samples should be taken into consideration. Thus, the ages of the earliest hearth structures in Klissoura cave are certainly older than the central European Gravettian with its clay technology dated from about 28 to 26 ka BP.
In their study of the lower Aurignacian hearths of Klissoura, Pawlikowski et al. (2000) suggested that the structures were probably the oldest evidence for the emergence of ceramic technology.
Figure 4 – a) Well-preserved superimposed clay structures from the lower part of the Aurignacian sequence of Klissoura cave. b) Clay structures as seen on the profiles. c) Detail of a thickened clay rim
In the field, the clay structures are distinguished as distinct dark red compact features with a basin-like shape (Figures 3 and 4a, b) that occasionally overlie one another. Where they overlie each other there is no disturbance of the lower structure, but the new hearth is built upon the truncated underlying one (Figure 4a, b). Their diameters are about 30 to 40 cm and some of them preserve a prominent thickened clay rim (Figure 4c). Some of the structures are fragile and a few of them disintegrate into fine-sized aggregates. However, some of them when moistened become soft and partially retain the clay plasticity.
The hearth structures are found beneath greyish burnt remains composed of loose ash,
charcoal fragments, reddened soil lumps and large amounts of burnt bone fragments and lithic artefacts. Sometimes thick stratified burnt remains separate a series of hearth structures (Figure 3). The boundary between the hearth structures and underlying ashes is sharp, straight and smooth (Figure 5a). However, the upper boundary is not so obvious and only a straight dark line separating the overlying burnt remains is sometimes visible (Figure 5a). In the case of Hearth 50, layer IV, the top millimetre of the upper boundary has a darker red colour as compared to the rest of the material. Hearth 41, layer IV, seems to consist of at least three distinct sub-layers of a thickness of 2 cm each (Figure 5a). Their boundaries are sharp, clear, and also delineated by a dark line. All the sub-layers contain a few visible coarse fragments of variable composition.
Using micromorphological techniques it was possible to examine five of the hearths (no 12: layer IIIc, no 41: layer IV, no 50: layer IV, no 63 and 63a: layer III’’) and their overlying and underlying burnt remains. Under the microscope the lower boundaries of the clay structures appear straight and mostly sharp (Figure 5d). The burnt remains are loose and porous, whereas the overlying clay structure is compact and massive. There is no sign of disturbance or mixing of the two contrasting materials. The upper boundary is locally more diffuse at a microscopic scale (Figure 5b).
The body of the hearths is composed mainly of reddish clay with a dense and very homogeneous appearance and with very little porosity except for a few dispersed vesicles and large voids (Figure 6a). In most cases prominent horizontal fissuring is present that also bears signs of ferruginous coatings. Such a feature cannot be attributed to artificial cracking during the excavation, or be due to the preparation of the thin sections, but should be related to the manufacture, or heating procedure.
The coarse component of the hearths consists of large amounts of evenly distributed fine sand- and silt-size chert fragments, quartz and, more rarely, exotic materials (schist, basalt, etc.) (Figure 6a). Note that no burnt remains, such as charcoal fragments or ash crystals, were found inside the clay layers.
The upper sub-layer of Hearth 41 differs from the lower sub-layer in that it is less decalcified, less clayey and contains less exotic materials. Many very fine plant imprints and some altered bone fragments are also observed in the matrix of this sub-layer.
The burnt remains above and below the studied structures consist mainly of lozenge-shaped calcitic crystals attributed to wood ash crystals (Figure 5b). The presence of some plant pseudomorphs of calcitic ash suggest minimum disturbance of the burnt remains. Burned soil lumps, charcoals and a large amount of bone fragments showing varying degrees of burning are important attributes of the burnt remains.
Figure 5 – Polished resin-impregnated slab of a section of a clay structure and the enclosing sediment a) and microphotographs of their contacts: b) Upper contact showing light grey ash crystals impregnating the underlying clay structure. Note the dark appearance of the clay aggregates due to burning (crossed polarised light). c) Contact between two sublayers of the clay structure marked with ferrougineous coatings (black) and large polyconcave voids (white) (plane polarised light). d) Lower contact between the dense clay structure and the underlying porous burnt remains (plane polarised light)
The main evidence that supports an intentional preparation of the clay hearth structures is:
• The shape and dimensions of the clay structures are more or less constant. In particular the clay rims of the structures strongly suggest an intentional construction.
• The geometry and characteristics of the boundaries of the structure are straight and smooth and there is no evidence of erosional contacts, despite the juxtapositioning of very different materials.
• Some structures consist of homogeneous, distinct, and unique sub-layers, each one implying a different and homogeneous natural source of material.
• The source of the material of some of the sub-layers that make up the structures is derived from an area away from the cave.
• No evidence for any kind of natural process that can account for the formation of the hearth structures was found. In particular, there is no sign of incorporation of any burnt component inside the clay structures that would imply colluvial or rain-wash processes.
The obscure horizontally layered structures in parts of the hearths and the vesicular porosity are characteristic puddling effects from wet conditions of manufacture (Courty et al. 1989: 125). The ferruginous boundaries between the different sub-layers of the structures, as well as the large polyconcave voids also lined with ferruginous material close to the boundaries, imply iron movement under conditions of water saturation (c.f. Courty et al. 1989: 151-153; Bullock & Thompson 1985: 41). However, cave moisture absorbed by the clay after being heated may have also played a role in the movement of iron (Macphail R., 2004, personal communication). The clay material was brought to the site and after wetting it was carefully puddled and shaped in place. It is not sure if the plant material in some of the sublayers was deliberately added as a stabilising material. The plant imprints are generally shorter than a few millimetres, something that is normally not found in more recent analogues. From the hearth structures studied it seems that there were not more than two or three reconstructions or repairs. In most cases the hearth was filled with ashes and a new hearth was built above the old one.
There are no signs of intense heating of the hearth structures. Microstructural changes, such as the formation of a glassy phase, or a loss of most of the original clay characteristics, have not been observed and the inherited pedogenic features seem to be intact. FTIR and DTA experiments suggest that the clay structures were heated to between 400 and 600°C, which are typical surface sediment temperatures generated by campfires (Bellomo 1993). Moreover, the clay hearth structures are quite friable and cannot be moved without breaking into small pieces. Actually, there are clay structures that still retain some of their original clay properties after being wetted. It is therefore reasonable to assume that the clay was not prefired.
The undisturbed burnt material associated with the hearth structures suggests that the primary and probably the only use of these structures was as firing or cooking places. Indeed, the calcined appearance of the top of some of the structures and the associated large amount of wood ashes, burnt bones, burnt plant remains and seeds (Koumouzelis et al. 2001) support this interpretation. However, we were usually not able to precisely differentiate in the field the boundary between the contents of the clay structured hearths from the rest of the interstratified ash remains. In contrast, under the microscope it was possible to define the undisturbed part of the ashes that are associated with the structures and confirm the existence of burnt bones and charred material inside them. In addition, one of the few samples that were collected from the content of the clay hearth structures yielded phytoliths of starches of seed grasses (Hearth 18), probably of Graminae, which suggests that the structure was used for roasting grains of wild grasses.
Most of the bones associated with the hearths are of fallow deer and hare and of the birds Rock Partridge and Great Bustard. Burnt seeds of edible plants like Chenopodium sp. (goosefoot) and fruits of Polygonum sp. (knotgrass) were identified in the upper Aurignacian layers (Koumouzelis et al. 2001), but it is not possible to determine if they were being cooked.
The picture of the Aurignacian hearths differs substantially from those of the Middle Palaeolithic. The Middle Palaeolithic hearths are unstructured and composed of colourful sequences of alternating thin white ash layers and black charcoal-rich layers that represent discrete repeated episodes of burning (cf. Courty et al. 1989). The preservation of these discrete intact features can be attributed to the absence of trampling and probably the intermittent use of fire. One possible explanation would be that visits to the site were infrequent or spasmodic. In contrast, the thick accumulations of ash in the Aurignacian layers might imply more intense occupation and more continuous use of the fires. The associated large number of clay hearth structures is consistent with this possibility. Interestingly, clay structured hearths were not found in any of the layers overlying the Aurignacian.
The data from the Klisoura cave show that new aspects of fire-making activities are introduced at the beginning of the Upper Palaeolithic. The use of clay in the beginning of the Aurignacian in the Klisoura cave 1, Greece, at about 32-34 kyr BP, precedes the manufacture of clay figurines and kilns in Dolni Vestonice and the Middle Danube Gravettian (Pavlovian) dated to 26 kyr BP.
(Source: “The earliest evidence for clay hearths: Aurignacian features in Klissoura Cave 1, southern Greece”, by P. Karkanas et al.)
Figure 6 – Microphotographs in crossed polarised light of a) clay structure showing chert (white-dotted crystals) and quartz fragments of sand and silt sizes (white crystals) in a striated clay matrix, b) terra rosa soil with silt-size quartz (white crystals)
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