Space, karstic Shelter and Digital Meaning

Ana Cruz, Polytechnic Institute of Tomar, Hugo Pires, Faculty of Architecture of the University of Porto (CEAU), Zélia Rodrigues, University of Coimbra, and Fernando Pimenta, University of Porto

Keywords: skyscape; structural orientation; identifying post-depositional features in karstic environments

This abstract represents a study related with post-depositional features in karstic environment. The fieldwork methodology requires a training camp to find the differences between a collapsed and a non-collapsed burrow. Roots cross sediments, small mammal and reptile galleries destroy a portion of sediments, human primary inhumations with reduction had a large impact.

In central Portugal, along the watershed of Nabão river, one finds a karstic complex shelter with Neolithic, Chalcolithic and Early Bronze Age funerary uses.
The route to this complex follows the archetype of initiation: the visitor leaves behind a wide and open horizon and descends into a narrow valley – Nabão river meanders – to reach the caves. The complex is composed of two caves layered one on top of the other: Lower Morgado below Upper Morgado. The Upper develops along three circular chambers of decreasing size, aligned along the same axis. The arrangement is like that of a portal that would allow a passage between different worlds, as probably the American natives (Krupp 1997) or the Australian aborigines would conceive it (Rappenglück 2007).
In the first chamber, close to the South wall, over 250 deceased of both genders, children and adults, were buried with fragments of speleothems, calcite crystals and river pebbles. Large speleothems close off this disposal area (Cruz et al 2018). Bones in this area were dated between 3500 and 2600 BCE, from Chalcolithic and Early Bronze Ages. In the second chamber two Neolithic burial periods were found: the first dated to 4850 BCE and the second to 4000 BCE. During the later period the older remains were moved to the sides and the center of the chamber reused.
This second chamber provides a more constrained view to the external landscape and, consequently, skyscape. This view would frame the rising Equinoctial full moons, particularly “the” Autumn full moon (Pimenta 2016), which is the first autumnal full moon after the rising sun and full moon swapped positions in the horizon (Silva and Pimenta 2012). Antares ( Scorpio) was visible from this chamber, between 5000 and 2700 BCE, rising in the axis of the cave around 4000 BCE. It was visible from the Autumn equinox until just before the Spring equinox, during the flooding period with difficult the access to the cave by the river. From Chalcolithic and Early Bronze Age burial area, in the first chamber, it would not be possible to see the rising of the Equinoctial full moons nor Antares. However, the Summer solstice sun would be seen rising over a facing hilltop.
This could be evidence of a cosmological shift from a lunar or stellar emphasis at Neolithic to a solar one in the Chalcolithic and Early Bronze Age, which could also correspond to a shift of interest in the seasons of transition (Spring and Autumn) to Summer. In Portugal, whose subsistence economies have been since the Neolithic largely tied to pastoralism (Senna-Martinez et al. 1997; Cruz 2001), it is no wonder that one may find alignments to celestial events that could mark key seasonal moments in the transhumant cycle.
Further into the cave, inside the third chamber not yet excavated, a light effect takes place over an artificially placed speleothem which is illuminated by the light of the rising sun at the Equinoxes. This possible light hierophany occurs about two days after the spring equinox and two days before the autumn equinox – dates corresponding to a conception of equinox obtained by halving the number of days between the solstices (Esteban and Cabrera 2005), as found in several pre-Roman cave sanctuaries of the Iberian Iron Age, like Cueva de la Lobera (Esteban et al 2014).
Different social groups at different periods may have recognized the sacred character of the cave and re-used it, organizing the space according to their beliefs, destroying, not recognizing or ignoring the symbolism of previous occupations.
Interpreting single sites such as this is risky because these “alignments” may be merely due to chance, but evidence suggests these communities had similar structure and spatial organization as communities of Alentejo (Da Silva 2004; Pimenta et al. 2009) and Mondego basin (Silva 2013; Silva 2014; Silva 2015) that built and used megalithic graves.

Archaeological sites located in karstic environment are the most complex when intervened. The field experience obtained in Caldeirão Cave (Zilhão 1992) (Tomar) and Ave Casta cave (Ferreira do Zêzere) (Mateus 1982), had its culmination in other interventions in limestone area: Cadaval Cave, Ossos Cave, Nª Sr.ª das Lapas Cave (Cruz 1997; Cruz 1991; Cruz, 2000; Cruz and Oosterbeek 1983; Cruz and Oosterbeek 1985; Cruz and Oosterbeek 1988; Cruz and Oosterbeek 1993; Cruz, Oosterbeek and Pizzioli 2000; Cruz, Graça and Oosterbeek 2014; Oosterbeek 1985; Oosterbeek 1987; Oosterbeek 1987b; Oosterbeek 1992; Oosterbeek 1993; Oosterbeek and Cruz, 1990), and Upper Morgado Shelter (Cruz 1997; Cruz 2000; Cruz et al. 2018; Cruz et al. 2013; Cruz 2016; Cruz 2016a; Cruz and Berruti 2015; Cruz and Cerrillo-Cuenca 2015; Cruz and Oosterbeek 1988; Oosterbeek 1987a; Oosterbeek and Cruz, 1990; Oosterbeek and Cruz 1998; Oosterbeek et al. 2000).

Working in karst cavities for years one learned a methodological lesson about basic procedures: a) “see” = deduct; b) “look” = consider; c) “observe” = ponder; d) “identify” = indicate the nature and distinguishing characteristics; e) “verify” = demonstrate; f) “to intervene” = to correlate.
These procedures can be considered commonplace but, without these tools, the clear and undoubted identification between the sedimentary space that is in situ and the sedimentary areas that are identified as disturbed “either cultural or natural”. The post-depositional variations are very difficult to identify by the common excavator when trying to define and identify changes in sediment texture and structures morphology (positive or negative) (Knüsel and Robb 2016).
The major methodological problems facing cave dwellers are post-depositional phenomena such as diagenetic processes that dissociate human findings and challenges from their primary context (Stratford 2011; Nehme et al. 2018).
Thus, this features are dedicated to the taphonomic phenomena on bone (human and fauna), intra-lithologic aspects of the cavities, biological ones and anthropization (vandalism, plunder, funerary occupations not identified with previous burials), whose seriousness result is directly related with the longevity of the funeral occupation.

Several software tools were used, enabling virtual visit to the shelter, historical documentation of the excavation and support of further analysis.
3D scanning was used to virtually recreate the entire site, reproducing the original shape and dimensions, allowing virtual inspections and geometric calculations. Control points in the shelter’s surfaces were surveyed, followed by sets of photographs with large overlapping. A photogrammetric model was built, and dense point clouds calculated to describe the shelter’s surfaces. Color information was re-projected to a triangulated mesh. This process was repeated for each phase of excavation for 4D representation.
Horizon software was used to create panoramas, without vegetation obstruction and atmospheric haze, from one arc-second SRTM data. These panoramas were used with Stellarium software producing past sky simulations.
The 3D photogrammetry model was georeferenced and used with Scenery3D allowing the virtual user to walk around and explore the scenery as well as displaying light and shadows cast by sun or moon.