Irmela HERZOG | Sandra SCHRÖER
(The Rhineland Commission for Archaeological Monuments and Sites, Bonn, Germany)

Keywords: Least-cost path, Thiessen polygons, Roman roads, southern Germany

The initial aim of this project was to reconstruct the boundaries of the Roman administration units in a large part of southern Germany based on known central locations and least-cost Thiessen polygon calculations. The boundaries derived from SRTM elevation data by applying the popular Tobler cost function roughly coincide with those of standard Thiessen polygons even in hilly regions. These results do not change significantly when assigning high costs to crossing the main rivers or when choosing a slope-dependent cost function for vehicles rather than for pedestrians. For this reason, we decided to investigate the issue more thoroughly in a small part of the study area. For this area, we mapped indicators of boundaries and some traditional road reconstructions of Roman roads. The known Roman roads allow estimating the costs of movement during Roman times in this part of Germany, i.e. for several cost models, least-cost paths (LCP) were compared with the routes of the known Roman roads. Based on the best performing cost model, accessibility maps were created. Some evidence is presented that most Roman boundary sections can be found in areas of either very low or very high accessibility suggesting that natural boundaries are more important than the equal distances principle motivating the Thiessen polygon approach. Some issues detected in the course of this research will be discussed, e.g. the difficulties of attributing appropriate costs for crossing the rivers and creeks based on the available data on modern water bodies.