Provenance determination of buntsandstein artefacts from the early-medieval dorestad trading site (the Netherlands): an example of the significance of geological-mineralogical analysis in archaeology

Abstract

From the Early-Medieval Dorestad trading site (The Netherlands) which flourished between AD 700 and 850, artefacts made of a variety of rock types were excavated. The rich suite of Early-Medieval object types includes querns, mortars, weights, rotating grindstones, cup-like objects and a Roman altar stone which are partly or completely made of Buntsandstein raw material. Other Early-Medieval artefacts such as whetstones, sarcophagi, touchstones and wells do not consist of Buntsandstein material at all. The suite of Late-Medieval objects which is found at the same place includes sarcophagi, cannon-balls, mortars, roofing-tiles, disc-shaped objects and ornamental stones which exclusively consist of materials other than Buntsandstein rocks. The provenance regions of the various lithofacies comprise near, moderately far and very remote areas. Petrographical analysis of the Buntsandstein samples deriving from both artefacts and accompanying stones without working traces makes it possible to distinguish nine rock types. Rock types I and II which occur most frequently are assigned to the Middle Buntsandstein Karlstal-Schichten and the Upper Buntsandstein Kyllburg-Schichten and Voltziensandstein of the Eifel, respectively. Rock type III which is only represented by two rotating grindstones among the artefacts is correlated with the Middle Buntsandstein Solling-Folge in the Solling. The other rock types cannot be assigned to specific provenance regions, but these are quantitatively of very minor importance. In the light of the petrographical results, the distribution of lithologies among the Buntsandstein artefacts from Dorestad is shown to vary with object type which indicates several source areas for the material deriving from the Buntsandstein; this could imply that the material was already partially introduced in worked condition to Dorestad. The presence of the large Roman altar fragment, however, suggests that a considerable amount of the artefacts consisting of Eifel Buntsandstein material was made by the Early-Medieval men from objects which were already imported into The Netherlands by the Romans. The conclusions concerning provenance of most of the Buntsandstein material from the Eifel based on petrographical results are further supported by logistical and archaeological evidence. The most important of the indirect criteria are the presence of several rock types of volcanic origin also coming from the Eifel and the fact that the Eifel is the geographically nearest and logistically easiest accessible source for Buntsandstein material from Dorestad. Another supporting point is the long history of Buntsandstein exploitation in the Eifel which dates back to Roman and even Celtic times. Different grain sizes of the sandstones from which the artefacts are made demonstrate that the material does not derive from only one locality for each formation, but comes from several source quarries spaced nearer or further apart. This is also supported by the presence of bleached samples which are interpreted as having been quarried already in discoloured state. Colour conversions to uniformly grey or bright, fire-like red at the surface of some artefacts testify to changes by heating during use or further bleaching by treatment with liquids or percolating waters after burial within the archaeological strata. The provenance of the raw material for the predominant amount of the Dorestad Buntsandstein artefacts from the Eifel indicates that it derived from different regions within one main source area, with only minor additional contributions coming from various other regions or even local sources. The provenance determination of the Dorestad Buntsandstein material is an outstanding case study of the significance of application of geological-mineralogical methods for unravelling archaeological problems and relationships.