Megalith-Building, Stone Transport and Territorial Markers; Evidence from Vale De Rodrigo, Evora, South Portugal
Kalb, Philine, Antiquity
A further contribution concerning the moving of the great stones used in megalith-building in later prehistoric Europe.
Some years ago R.S Thorpe & O. Williams Thorpe (1991; 1992; Thorpe et al. 1991), generalizing from the case of the Stonehenge bluestones, concluded there was no 'long-distance transport' at all of megaliths. Rather, megalithic monuments were built on sites where the materials for construction were easily available; and Renfrew's thesis (1976) about megaliths as territorial markers is denied validity. Patton (1992) shows, from geological investigations on the Channel Island of Jersey (Mourant 1933), that some rocks for the construction of a megalith were transported over a distance of more than 5 km, the distance Thorpe & Williams Thorpe think the maximum for local transport of megaliths. He thinks the Jersey tomb of La Hougue Bie very well could have marked a territory: it occupies a privileged position in comparison to other smaller monuments, and the choice of a dominating place is determined by other reasons than the existence of construction material. Stone was brought from near the coast to La Hougue Bie, over a distance of several kilometres. One upright was even brought from the 7-km distant Mount Mado.
Rocks and their sources in Evora megaliths
In southern Portugal there was no glaciation at all, and no erratic boulders were available for the construction of the more than a thousand megalithic tombs. Geological investigations about the megaliths of Vale de Rodrigo, near Evora, have shown that surface rock was used for constructing monuments in this region; big blocks or plates were extracted at places with natural clefts in the rock. Different rocks have been transported over distances up to at least 10 km [ILLUSTRATION FOR FIGURE 1 OMITTED]. This long-distance-transport and rock selection seem to have been important to the very construction programme of the megalithic monuments (Dehn et al. 1992).
In Vale de Rodrigo four monumental tombs are situated near together. In each, several kinds of rock are used for construction of the chambers - e.g. biotite-tonalite, biotite-hornblende-tonalite, and porphyritic granodiorite. None of these is of local origin; the subsoil is formed by gneiss. Biotite-tonalite and biotite-hornblende-tonalite can hardly be distinguished with the naked eye, even by an expert. For the selection of one or the other as construction material, the look of the stone can hardly have played a role. Biotite-tonalite which occurs 1-2 km west of Vale de Rodrigo predominates as construction material in the three still preserved monuments. The biotite-hornblende-tonalite, used less, occurs in the east of Vale de Rodrigo, somewhat nearer but beyond a small river. Explanation of the choice probably lies in the nature of the stone: the biotite-tonalite west of Vale de Rodrigo, with more clefts than the biotite-hornblende-tonalite east of Vale de Rodrigo, is more suitable for extraction of big plates or blocks. Porphyritic granodiorite occurs 7-8 km to the north or 6-7 km to the east of Vale de Rodrigo; it must have been transported from there. It is easy to distinguish from the other rocks by its conspicuous large, white crystals of feldspar. Its appearance could have played a role in the choice; but there are no regularities recognized in the position of stones of this material in the constructions.
The Menhir at Vale de Rodrigo 1, weighing about 15 tonnes, as well as one upright of this tomb, are of a kind of granite that occurs only at a single place in the region, 10 km distant from Vale de Rodrigo. The two blocks must have been brought from there, crossing at least two brooks. The use of blocks from far away is characteristic of the large monuments of Vale de Rodrigo, while the smaller monuments in this area are usually constructed with blocks from near-by and of only one type of material.
Rocks and stone found in other Iberian megaliths
Use of different rocks in the same megalithic construction can also be observed in other areas of the Iberian Peninsula, such as Crato, district of Portalegre, Portugal (where geological investigations about stone sources are lacking). …