Proving a Roman technical masterstroke: GIS-based viewshed and intervisibility analysis of the Bavarian part of the Rhaetian Limes

The direct visibility between watchtowers and their corresponding fortresses in the hinterland was a crucial factor in the effective protection and control of the Roman frontier. Solely, archaeological excavations cannot evaluate these interactions in detail. Hence, modern geoinformatics can help with a fast and easy approach to gather information about such line-of-sights by a viewshed analysis in GIS. There is a huge amount of literature dealing with Roman watchtowers, but only a few approaches using GIS-especially in the German parts of the Roman frontier-have yet been made. Here we present such an approach for the whole Rhaetian Limes in Bavaria. Along with an overview of the complete route of the frontier, three local case studies are shown that tackle specific issues related to understanding the functioning of these defensive systems. The first one deals with the perfect direct intervisibility between five adjacent watchtowers along the frontier line. Secondly, an up to now missing watchtower within the modern woods can be quite surely located by airborne laser scanning. Nevertheless, only a ground truthing by excavating the watchtower at the proposed location would give certainty. The last case study provides a possible solution for the long-lasting debate of the signal transfer between two adjacent fortresses with a mountain in the direct line-of-sight.

Automated summary

Using geoinformatics and GIS viewshed analysis, this study presents an approach to understand the visibility between Roman watchtowers and fortresses along the Rhaetian Limes in Bavaria. It also includes three case studies that address specific issues related to the functioning of these defensive systems.