The prehistoric rock art of the western Iberian Peninsula has steadily grown in prominence over the past 40 years. Initially, this interest centred on images found in Neolithic dolmens and passage graves, but a new focus appeared during the early 1990s, with the scientific discovery and study of remarkable open-air Upper Palaeolithic rock art in the Côa Valley and its tributaries in north-east Portugal (see CWA 67). But what about rock art elsewhere in this part of the Iberian Peninsula? Over the recent past, successive Portuguese governments have successfully promoted hydroelectric power and, as a result, many of the major river systems in central and northern Portugal have been dammed. The Tagus River Basin presents a classic example of this trend. It was along this great river system that prehistoric rock art from various eras was detected in the early 1970s, with the discovery of an Upper Palaeolithic equid known as the ‘Ocreza horse’ following in 2000.
A long legacy
The Tagus Rock Art Complex, located in central Portugal, covers an area of some 120km of riverbank and terracing, which includes 12 known rock-art clusters, located between the mouth of the Ocreza River (downstream) and the Erges River valley (upstream). These clusters include a total of 1,636 engraved rocks featuring around 7,000 recorded images that range in date from the Upper Palaeolithic to the Late Bronze Age (between the 20th and 2nd millennium BC). The Tagus rock- art assemblage comprises mainly animal engravings and geometric motifs. A limited number of human figures are also present, though, with the vast majority showing farmers and herders that date to the Neolithic and Chalcolithic periods. In addition, there are a further 200 figures and motifs that were created by Mesolithic hunter-fisher-gatherers. There is one figure recorded by the authors in 2013 that shows a probable pregnant female horse in a running stance that dates to the Upper Palaeolithic. This early pecked horse is found within the lower terracing of the Ocreza Valley, one of the many tributaries feeding into the Tagus River. Other animal images can be dated to the Mesolithic period and include red deer, goats, horses, ibex, and several wolves.
Although the first engravings were officially discovered in 1971, it seems likely that the communities living within the Tagus River Basin, especially the local fishermen, had known something about this rock art for generations. All of the engraved art detected so far was created by striking the rock with a pointed tool such as a hammerstone, a method known as the ‘pecking’ technique. Currently, most of the visible images can be found on river-worn smooth schist that occupies the bank edge. Before the Tagus River Basin was flooded by the construction of a dam, though, this outcropping rock stood proud, some way from the water’s edge.
The rock art was discovered by members of an archaeology team from the National Museum in Lisbon, who were carrying out surveys of local quaternary geological formations in advance of the dam project. Their survey stumbled on ‘written stones’ located on the banks of the Tagus River, close to the train station at Fratel. As a result of this chance encounter, the rock art was photographed. It was clear, though, that more systematic survey was needed – and urgently. Work on the dam was already under way and could not be halted, while completion of the structure would be followed by the water level rising until much of the rock art was submerged, leaving it inaccessible to future generations. The challenge, then, was for archaeologists to both identify rock-art clusters and think up a system that could accurately and rapidly record both individual motifs and complete panels, so that detailed study could take place off-site.
Successful experiments with liquid latex elsewhere in Europe indicated that this could be used to create a negative impression of rock surfaces engraved with art. Technical guidance on how to use liquid latex for this purpose was provided by the French prehistorian Michel Brézillon. In 1972, members of the Tagus field-team were invited to Paris, where they met with rock-art specialists André Leroi-Gourhan and Annette Laming-Emperaire. Once assured of its potential, the Tagus team, under the direction of Eduardo da Cunha Serrão, decided to apply the liquid latex method.
A race against time
An emergency recording programme began during the construction of one of the dams – the massive Fratel Dam. This water-management project was set to raise the water level of the Tagus River and its tributaries sufficiently high to submerge most of the significant archaeology along its banks, with the exception of some outcrops of schist rock with engravings.
Using the latex-mould method rather than a more traditional tracing technique significantly reduced the recording time required for each rock-art panel. As a result, many images engraved along the Tagus River Basin were successfully recorded. The liquid nature of the latex allowed the impression of even the smallest natural cracks and fractures to be captured. Even so, during the fieldwork it was decided to plug large natural fissures in the rock face with plasticine before the latex was applied. Today, we can appreciate that a drawback to this approach is that it distorted the true nature of the surface – an important consideration given that the creators of rock art sometimes used natural features to enhance certain figurative elements. Where possible, complete panels were recorded using a single latex mould. Such standardisation also allowed ease of transportation and storage. Another benefit of using this recording method was that it removed any risk of the process being skewed by subjective personal readings of what the images seemingly showed. As the latex mould provided a faithful rendering of what was present, there was less need for any archaeological interpretation during the recording process.
The first step when creating a mould was to prepare the rock surface, by defining the extent of the art and cleaning the area around it. Due to the seasonal changes in water levels, some panels were covered by algae, lichens, and debris. Next, several layers of liquid latex were applied to the rock surface. This creamy-white fluid has a slightly milky consistency and contains about 70% dry rubber, as well as a low percentage of ammonia to prevent the liquid from coagulating. Each layer was formed by simply allowing the water to evaporate, creating a vulcanised rubber film. In between the layers, a gauze membrane was inserted in order to give the mould consistency and movement. Additional latex layers were then applied until the required thickness was achieved. Once dry, the layered mould would be carefully removed, referenced, and stored. Ultimately, this process was repeated for nearly 1,500 rock surfaces.
Recording rock art in the laboratory
Any attempt to study the rock art of the Tagus River Basin today owes a great debt to all those who raced against time to record the images. While the inundation of the river makes it impossible to search large areas of the basin for art that was overlooked in the 1970s, the latex moulds probably provide an excellent representation of the overall thematic assemblage. Once these impressions had been made, they remained largely in storage for the next 45 years and were not systematically studied. There matters rested until a little over a decade ago, when an assessment of the preservation of the moulds was undertaken. The verdict was generally good. Given the potential of this archive, one of the authors (Sara Garcês), decided to undertake a long-term detailed recording project of the images using more conventional methods.
After the moulds had been gathered from the various repositories holding them, our methodology involved several steps. First, we created a formal registry of all 1,464 latex impressions created during the rescue programme. In the overwhelming majority of cases, it was possible to say roughly where each mould originated. The latex archive includes moulds from ten sites: Alagadouro, Cachão de São Simão, Cachão do Algarve, Chão da Velha, Ficalho, Fratel, Foz de Nisa, Gardete, Lomba da Barca, and Ocreza. There are also a further 20 moulds that were identified as ‘No Station’ because their location on the Tagus River was not correctly noted at the time of fieldwork recording. Next, each mould was traced using transparent acetate sheets, with oblique lighting employed to bring out maximum detail.
All the traced acetate sheets were then digitised, creating a vast virtual archive. In many cases, reconstructing a complete panel involved marrying several tracings together, which was achieved by ensuring that both digital and traced images had overlapping borders. When it came to placing this enormous assemblage of rock art into its virtual landscape context, we were fortunate that three sites located downstream of the Fratel Dam still remained partially above the waterline. While the three sites were recorded in the same manner as those clusters now only represented by latex moulds, the opportunity was seized to study how these engraved surfaces were distributed within what could be reconstructed of the prehistoric landscape.
In other cases, despite the accuracy of the recording methods employed by our team, we suspect that the precise location, orientation, and angle of slope of panels noted in the 1970s may be open to question. As with any complex jigsaw, the Mação team had to rely on multiple strands of evidence to reconstruct an accurate picture of each panel and the landscape in which it lay. Much of the evidence for the local terrain was supplied by photographs of the 1971-1973 fieldwork, shortly before many of the panels were submerged.
The final phase of our project involved creating a detailed photographic archive, undertaken in partnership with the Master’s programme in Photography at the Polytechnic Institute of Tomar and the Instituto Terra e Memória (Mação, Portugal).
As a result of this work, all known figures and motifs in the region have now been recorded by various scholars over the past 50 years. Despite this achievement, it has been estimated that at least 10,000 engravings remain unrecorded and underwater in the Tagus River Basin. It is hoped that careful monitoring of the region – especially when water levels are low – will permit more panels to be discovered, recorded, and accurately located.
Where does the Tagus rock art fit?
When considering the Tagus material, it is intriguing to compare it with the Upper Palaeolithic rock art discovered in the Côa Valley during the late 1980s. This later discovery did much to ignite interest in the Upper Palaeolithic heritage found in this part of Europe. It would be fair to observe that the unique material encountered in the Tagus River Basin some 20 years earlier initially attracted less international attention, with knowledge of its rock art remaining largely restricted to the local area. While the Côa Valley showcased Upper Palaeolithic art, though, the Tagus River Basin covered a much wider group of periods, with Mesolithic, Neolithic, Copper Age, and Bronze Age imagery, while the Upper Palaeolithic is represented by the Ocreza horse. Despite these different chronologies, the rock art in these two areas was created within what were effectively identical landscapes: exposed schist outcrops in deep V-shaped valleys beside great rivers.
So, what has our work revealed? Thanks to the recording programme in the laboratory, we can be confident that the Tagus River Basin rock art presents a well-defined chronological sequence from the Upper Palaeolithic to the Bronze Age, a period of at least 20,000 years of rock-art activity. Indeed, that is not the end of the story, as Roman inscriptions and modern text and images were also found engraved in the valley. The prehistoric art itself can be divided into several phases, with an important division between what is known as ‘Pre-schematic’ and ‘Schematic’ styles. Pre-schematic rock art largely comprises representational images such as goat, horse, ibex, red deer, and human figures, while Schematic rock art consists of geometric and abstract forms that were produced by Neolithic and Bronze Age farming groups. Of these, examples of Schematic art are noticeably more numerous than any other style.
Overall, the project has revealed a near-continuous use of rock art over a 20,000-year period, although clear breaks between styles can be seen. This was sometimes made especially obvious, when art of a later style was deliberately superimposed on top of examples created in earlier periods. More intriguing was the way rock art was distributed across the Tagus River Basin. For example, the three largest and most complex engraving sites are in places called ‘Cachão’ (meaning ‘rapids’). Prior to dam construction, it was at these places that access to the river and attempts to cross it would have been dangerous. Most of the other rock-art sites are located at the confluences of small tributary streams. Now that this has been observed in the Tagus River Basin, comparable examples of rock-art distribution within other major river systems have been identified in central and northern Portugal, as well as western Spain – including the Schematic rock art of the Guadiana River Basin.
Despite such parallels, the various artistic styles found within the rock-art assemblages of the Tagus River Basin are unique. Of these, it is the Schematic rock- art style of the Neolithic, Chalcolithic, and Bronze Age that seemingly brings us closest to glimpsing the mindset of the artist and his or her audience. The intricate pecked images of abstract curvilinear and geometric motifs suggest an association between the engraved rock, the image, the artist, and the audience.
All aspects of rock-art production and consumption were intimately connected through a divine supernatural force, which was probably believed to have originated inside the rock itself, allowing it to communicate stories by guiding the artist’s creation of pecked images. Thanks to the dedication of those 1970s archaeologists, the art that expressed these stories lives on and can now be appreciated anew.
FURTHER INFORMATION To discover more about the Tagus River Basin and its rock-art heritage, visit the website of the Museum of Prehistoric and Sacred Art in the Tagus Valley, Mação, at www.museumacao.pt.
ALL IMAGES: courtesy of Sara Garcês and George Nash, unless otherwise stated.