Rock Art in Portugal's Border Area

1. IntroductionThis paper follows our presentation at the International Rock Art Conference organised by IFRAO in Caceres (Spain) in 2015, in the meeting devoted to the scientific study of rock art. Under this thematic framework, other petroglyphs in open-air outcrops and in several stelae located on the plateau to the west of the river Erges will be object of future publications.Special attention is given to two cyclopean constructions, forming small shelters (Tapada da Foz and Foz do Ribeiro das Taliscas) in the valley of the river's flood zone. In the inside of the shelters pecked petroglyphs (Tapada da Foz) and incisions (Foz do Ribeiro of Taliscas) are preserved. The constructions date, at least of the first shelter, from pre-History (Fig. 1).The recording approach consisted of the combined application of photogrammetric techniques, for the three-dimensional representation of the construction of the two shelters, with morphological residual model (MRM) (Pires et al. 2014), to so depict the artwork from these two shelters. The advantages of this technique over traditional recording methods, in particular three-dimensionality, higher contrast depictions, objectivity, versatility and portability, have overcome the main difficulties in the identification and tracing of rock art experienced in previous studies (Henriques et al. 2011 and 2012).2. Location and environmentThe river Erges, whose source is in the Serra de Gata (Iberian Cordillera Central), defines the border between Portugal and Spain for a distance of over 50 km and crosses mostly metasedimentary rocks of the Neoproterozoic (610-542 Ma). However, in Monfortinho, it breaks through a crest of Armorican Quartzite (488-435 Ma) and, next to Salvaterra do Extremo and Segura (Fig. 2), focuses on granitoids of Tardi-Variscan orogeny (315-300 Ma), forming magnificent river canyons (Rodrigues et al. 2008). In the adjacent platform overlooking the river Erges on the west side appear folds of detrital deposits from the Eocene-Pliocene (50-2 Ma) forming flattened surfaces.This river, of torrential characteristics in winter and small flow during the summer, has a free regime except at the confluence with the River Tagus where it is submerged by the Cedillo dam. The valley, with very little human presence, has high natural and landscape values and has been partially integrated in the International Tagus Natural Park and in the Geopark Naturtejo from the Meridional Meseta, where several geo-monuments stand out, like the canyons of Monfortinho, of Salvaterra do Extremo and of Segura.In 2007, the river Erges was evaluated for the National Plan for Dams with High Hydroelectric Potential, but was not selected for investment. In 2005 and 2007 surveys have been performed independently by two different teams of archaeologists on the Spanish bank (Nobre 2008, 2009) and the Portuguese bank of the river (Henriques et al. 2011, 2013), resulting in the identification of 16 sites with pre-Historic rock art on outcrops, in a natural shelter (Abrigo Catarina) and in two built shelters (Tapada da Foz and Foz do Ribeiro of Taliscas).The graphic symbols present in those sites are dominated (Table 1) by anthropomorphous depictions, especially on the right bank, and circular shapes, mostly on the leftbank of the river Erges, which seems to represent a symbolic border. Apart from these there are also pecked 'clouds', cupules, incised linear figures, a possible zoomorphic figure and indeterminate motifs.More recently, two panels with red paintings were discovered in a natural shelter located in the fluvial canyon of Segura (Martins and Nobre 2013), located upstream. The iconography of these panels is dominated by 'points', mostly arranged in regular sequence, and a circular figure with rays ('sun shape').The identified petroglyphs and paintings in the lower reaches of the river Erges integrate, organically, into a wider graphic universe, of regional scale, spread over different sites and forms of representation (Bueno et al. …