Quantification and modelling approaches of geoarchaeological processes – The course, construction and collapse of the Carolingian canal Fossa Carolina Von der Fakultät für Physik and Geowissenschaften der Universität Leipzig genehmigte DISSERTATION zur Erlangung des akademischen Grades Doctor rerum naturalium Dr. rer. nat. vorgelegt von M. Sc. Geogr. Johannes Schmidt geboren am 08.12.1988 in Jena Gutachter: Prof. Dr. Christoph Zielhofer Prof. Dr. Hans-Rudolf Bork Tag der Verleihung: 19.04.2021 Dedicated to Luni „Denken and Wissen sollten immer gleichen Schritt halten. Das Wissen bleibt sonst tot and unfruchtbar“ oder „Die Natur muss gefühlt werden“ Alexander von Humboldt Abstract The European watershed runs across Europe and divides the river basins into a northern component and a southern component. Therefore, the river basins drain either northwards into the North Sea, Baltic Sea or North Atlantic, or southwards into the Mediterranean or Black Sea. There is no natural, fluvial connection between the North and South components. Between the cities of Weißenburg and Treuchtlingen in Bavaria, the Central European Watershed separates the catchment areas of the Rhine-Main System and the Danube System. The Swabian Rezat has its spring at the steep slope of the Frankenalb and runs northwards towards Weißenburg and drains into the Rhine-Main system. South of the European watershed flows the Altmühl, which drains into the Black Sea via the Danube. In the early Middle Ages, shipping routes were of the highest geostrategic interest and were used for military purposes in addition to the movement of people and goods. It was probably for these reasons that Charlemagne built a canal in 792-793 AD to provide a navigable connection (also known as Fossa Carolina). The Swabian Rezat and Altmühl rivers have a linear distance of ~2 km and the natural features (water supply, sedimentary architecture of the valley landscape, geological conditions) are almost ideal for the technical possibilities for canal construction in the early Middle Ages. The canal is of outstanding engineering quality. In the meantime, the canal has been filled in and is only visible in some places. In addition to archaeological, historical and geoscientific work, especially from the 20th century, an interdisciplinary research project has been investigating various aspects of the canal in since 2010. The focus of the research so far has been on proving the actual course of the canal, the archaeological documentation of specific finds and features of the canal and its surroundings, the history of the sedimentation of the canal, and the investigation of structures accompanying the construction. Furthermore, research was carried out on the archaeological and historical classification of the structure in the history of canal constructions. The decoding and comparison of geoarchaeological finds and processes is characterised by qualitative approaches. The description and documentation of a phenomenon and the way in which it manifests itself are usually the main focus. In recent years, however, methods have been developed from the disciplines of archaeology and archaeometry, geosciences and geoinformatics which serve to quantify geoarchaeological processes in the narrower sense in relation to monuments, but also in the broader sense in relation to landscapes. The aim of this work is to quantify individual processes of planning, construction and the collapse of the Fossa Carolina. High-resolution digital elevation models usually have the disadvantage that anthropogenic structures produce artefacts in the data which, although they represent the current surface, do not allow for natural- landscape-related, hydrogeographic calculations. A modelling of the pre-modern relief has been achieved by precise elimination of anthropogenic structures such as roads, buildings, railway lines, etc. The data basis is provided by official geodata of the State Office, OpenStreetMap and the historical cadastre I boundaries recorded in the beginning of the 19th century. For the semi-quantitative verification and validation of the modelling results, paleo-surfaces were recovered from drillings. The high-resolution pre- modern digital elevation model for the area around the Fossa Carolina allowed the calculation of the shortest hypothetical canal course. This is similar to the built original, conspicuously S-shaped and proves the topographical dependence of the canal construction. Hydrogeographic indices, such as the topographic wetness index, were used to justify the deviations of the actual canal course from the ideal line. It has demonstrated that the Carolingian builders had a comprehensive knowledge of the natural features of the area. They deliberately avoided wet areas with high groundwater levels and organic sediments, which would have been too unstable for the earthworks of the canal. Approaches to combine different geoarchaeological and geophysical methods and are not unknown, but mostly qualitative in nature. The previous investigations and analyses at the Fossa Carolina were combined by a new integrative and quantitative approach. Geometric and stratigraphic results from 3 archaeological excavation sections, 39 core drillings, as well as 2 direct push sensing transects with 105 colour logs were included. The resulting numerical 3D-model of the state of maximum excavation of the approx. 3 km long canal allows for the first time the calculation of the total excavation volume. Almost 300,000 m³ of material were moved for the construction. In contrast, the excavation dams that are still visible today, have a total volume of only approx. 120,000 m³. Therefore, almost two thirds of the total excavated material are no longer preserved in the dams, but have been eroded or removed since the end of the construction. Moreover, the excavated volume is not evenly distributed over the entire course of the canal, but the main part is located in the area of the Central European watershed. The 3D-model also allows the calculation of the trench bottom level of the longitudinal section of the canal. Thereby the summit zone of the stepped canal was identified. The basis of the infilled sediment of the canal trench is formed by sediments that have initially slipped back from the excavation walls (so-called backfills). Stratigraphically, they are accumulated directly on the canal trench bottom. A systematic evaluation of the geochemical and stratigraphical findings could show that the backfills can be declared as initial collapse sediments. Radiocarbon dating of macro remains date the backfills around the construction period 792/793 AD. Dendrochronological analyses also show that the timber used in the Fossa Carolina were felled and used in the years 792 AD and 793 AD. The spatial analysis of the felling ages also shows that construction progressed from north to south. The absence of still water sediments on the canal trench floor and the timber serve as a chronological framework and provides relative dating of the backfill sediments. Subsequently, the application of the 3D-modelling approach was transferred to the backfill sediments. The resulting spatial and quantitative distribution of the backfills along the entire canal course shows the concentration of these sediments in the Central Sections around the Central European Watershed. Sediment budgeting, as applied in geomorphology, could now be applied adaptively to the backfills. Nearly 35,000 m³ of backfill sediments were calculated in the Central and West- East Sections. This corresponds to approx. 15 % of the total excavation volume in this area. Therefore, these sections can be designated as a collapse zone. According to contemporary written sources, the canal II was abandoned due to unstable dams and back-sliding material. For the first time, the quantitative results provide a scientific proof for this hypothesis. In summary, this work is an example of the application of numerical and quantitative methods in the field of geoarchaeology and shows the value of these methods in understanding geoarchaeological processes and their reconstruction. III Kurzzusammenfassung Die Europäische Hauptwasserscheide verläuft quer durch Europa and trennt die Flusseinzugsgebiete in eine Nordkomponente and eine Südkomponente. Die Einzugsgebiete entwässern demnach entweder nach Norden in die Nordsee, Ostsee, oder den Nordatlantik oder aber nach Süden in das Mittelmeer oder das Schwarze Meer. Es gibt keine natürliche, fluviale Verbindung zwischen der Nord- and der Südkomponente. Zwischen den Städten Weißenburg and Treuchtlingen in Bayern trennt die Europäische Hauptwasserscheide die Einzugsgebiete des Rhein-Main Systems and des Donau Systems. Die Schwäbische Rezat entspringt an der Frontstufe der Frankenalb and verläuft nordwärts in Richtung Weißenburg and entwässert in das Rhein-Main System. Südlich der Europäischen Wasserscheide fließt die Altmühl, welche über die Donau in das Schwarze Meer entwässert. Im Frühmittelalter waren Schifffahrtswege von höchstem geostrategischem Interesse and dienten neben dem Personen- and Warenverkehr auch der militärischen Nutzung. Vermutlich aus diesen Gründen ließ Karl der Große 792/793 AD einen Kanal anlegen, welcher eine schiffbare Verbindung herstellen sollte. Luftlinie kommen sich Schwäbische Rezat and Altmühl auf knapp 2 km nahe and die naturräumliche Ausstattung (Wasserdargebot, sedimentäre Architektur der Tallandschaft, geologischer Untergrund) ist für die technischen Möglichkeiten des Frühmittelalters nahezu ideal. Der Kanal ist