Rock-art specialists George Nash and Sara Garcês reveal spectacular prehistoric paintings hidden in the burial chambers of central-north Portugal.
Thousands of late prehistoric burial-ritual sites litter the Atlantic façade of Europe, most dating to the 5th millennium BC, when first Neolithic and then Bronze Age pastoralists tended the fertile plains and valleys. These societies were steeped in ritual and symbolism, in particular with regard to their dead, who were buried in elaborately constructed dolmens. Today, many of these stone chambers lie in ruins, the result of historic agricultural practices and recent vandalism. However, a handful have escaped the ravages of time, most located within the now-secluded valleys north-west of the Iberian Peninsula. Many show clear evidence of painting within the passage and chamber areas: two of these, near Viseu in central-north Portugal, are among the most decorated on the peninsula.
In 2016, and again in 2017, as part of the newly established project to explore and document Neolithic and Bronze Age monuments that contain painted imagery, members of the Megalithic Art in Portugal (MAP) research project turned their attention to two well-documented painted megalithic sites using a new – but already well-tried and -tested – photogrammetric technique known as Decorrelation Stretch (abbreviated to D-Stretch).
This image software tool was developed for remote sensing by NASA in 1996, but was later enhanced by scientist Jon Harman to be used in rock-art prospection, specifically to manipulate the colours of rock-art images, particularly paintings. It is widely used by researchers engaged in the study of rock art. Optimum enhancement is usually achieved when photographing paintings that contain varying hues of red and yellow pigmentation. Our results from the two dolmens near Viseu are spectacular, and tell a very different story to that previously understood: suddenly, with the use of D-Stretch, the unique nature of once-hidden elements of painted geometric and symmetrical patterns sprang vividly from the chamber uprights of both monuments.
The first burial-ritual monument that we investigated for this project was the passage-grave of Arquinha da Moura, discovered in 1990, when the site was being used as a shelter by local hunters. Despite this modern-day recreational use, the passage and chamber – delineated by 17 large upright stones – remains in relatively good condition. Periodic covering by vegetation and soil formation has helped the survival of both the internal upright-stone arrangement and the cairn that surrounds the passage and chamber. However, damage had occurred to some of the painted images due to hunters lighting fires inside the chamber area.
The polygonal chamber area has schematic paintings on two of its seven uprights. We believe further painted images may well have covered other uprights. The site was subsequently excavated between 1992 and 1993, and flint tools, pottery, and items of personal adornment were recovered from the site. These artefacts are grave goods and were deposited to accompany the dead in their afterlife. The large assemblage of human bone found by the excavators suggests that successive generations of the community were interred, which is typical of passage-grave burials found elsewhere. Archaeologists discovered that the disarticulated human remains had been unusually grouped, with skulls on one side of the chamber and long bones on the other. Interestingly, the jaw bones and most teeth were absent.
Four of the stones are decorated using haematite (also referred to as red ochre), and traces of it were found on the chamber floor during excavation. A detailed inventory of Stone 7 revealed that four anthropomorphs were recorded, including a large male figure, a grid or net, and painted lines. On Stone 9, nine figures were identified: four anthropomorphs, two headless anthropomorphs, and three animal figures, including a caprid (goat).
Following the photographic survey, the team applied D-Stretch, which revealed a considerably more-detailed record of painted elements on the chamber walls. Though the conventional photographic record did show clear painted surfaces, the hues, pigment textures, and extent of each painted image was, in places, difficult to discern. The D-Stretch process, using a series of digital colour filters, teased out many of the hidden images, some of which had been absorbed into the rock surfaces.
Images: George Nash/Sara Garcês