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

Keywords: Historical maps; old roads; digital elevation models

According to a historical document dating back to 1065 AD, the Medieval road known as Strata Colonensis connected the monastery of Essen-Werden with Cologne in Germany. Two alternative hypotheses concerning the course of this route have been published, both agree on the southern part of the course between Hilden and Cologne. In their arguments, the supporters of both hypotheses refer to historical maps. The aim of the paper is to identify the most probable course of the Medieval road between Essen-Werden and Hilden by assessing the available historical maps and other sources, and by evaluating the geographical data in this region by appropriate GIS methods. Some details concerning the approach to be presented: The earliest map known to us that shows relevant road connections in this area is attributed to Henricus Hondius. This map was probably created in 1636 and was copied several times afterwards. Fortunately, the relevant map section could be accessed in two online archives free of charge. Georeferencing the early maps (including a map set finished in 1715) was not possible due to their distortion, instead these routes were transferred approximately to modern maps. Several Web Map Services show georeferenced map sets initially created in the 19th century. However, the accuracy of the earliest georeferenced maps is an issue. But often digitized roads on early maps coincide quite well with later routes on more accurate later maps. Moreover, typical archaeological approaches such as visualization of high resolution elevation data or aerial images could be used to identify old road sections in some areas. However, this is limited by substantial modern landscape modifications. Due to these changes, least-cost path analysis should not be based on modern geographical data in this area. But 19th century contour lines allow assessing the costs of the two routes.