Peter Ettel

Charlemagne’s Canal. An Early Medieval Project of European Dimension

by Christoph Zielhofer, Lukas Werther, Peter Dietrich, Stefanie Berg-Hobohm, Peter Ettel

The Central European Watershed divides the
Rhine catchment and the Danube catchment.
In the Early Medieval period, when ships were
important means of transportation, Charlemagne
decided to link both catchments by the construction
of a canal. The Fossa Carolina would
have provided a continuous inland navigation
route from the North Sea to the Black Sea.
Despite the important geostrategic relevance
of the construction it is not clarified whether
the canal was actually used as a navigation
waterway. 14C dating and sapropel layers reveal
evidence of Carolingian and post-Carolingian
ponds. Geoarchaeological drillings, high-resolution
direct-push-sensing equipment and
archaeological excavations indicate a conceptual
size of the canal, which allows a crossing
passage of Carolingian cargo scows with a
payload of several tons. Our results indicate an
extraordinarily advanced construction level of a
summit canal. We have evidence for the artificial
Carolingian dislocation of the watershed
and assume a sophisticated Early Medieval
hydrological engineering concept for supplying
the summit of the canal with adequate water.

Navigable canals are a rare exception in the Early Middle Ages, although ships were important means of transport. The Fossa Carolina is the most important exception and an outstanding example of Early Medieval hydrological engineering. It is located at the Central European Watershed between Rhine and Danube. Charlemagne decided to link both river systems in 793 AD. Despite the importance of the project it is not clarified if it was finished. The paper presents selected aspects and new results of a current research project towards the Fossa Carolina.

Um Schiffe, Waren oder Personen von einem Gewässersystem in ein anderes zu überführen, müssen Wasserscheiden
überwunden werden. Seit der römischen Kaiserzeit wurde versucht, die damit verbundenen Landpassagen durch
Kanalbauten zu umgehen. Im späten 8. Jahrhundert wurde mit der Fossa Carolina ein künstlicher Durchbruch der
europäischen Hauptwasserscheide in Angriff genommen, um die frühmittelalterlichen Hafennetzwerke an Rhein
und Donau zu verbinden. So einzigartig dieser Bau ist, steht er dennoch nicht isoliert: Schriftquellen liefern vielfältige
Hinweise zu Organisation und Ablauf größerer hydrotechnischer Bauprojekte und zeigen, dass künstliche
Wasserführungen im Frühmittelalter keine Seltenheit waren. Am Karlsgraben erlauben neben zeitgenössischen
Beschreibungen neue geoarchäologische, geophysikalische und archäologische Untersuchungen detaillierte Einblicke
in Bau und Unterhalt des Kanals. Diese werden für einzelne Bauabschnitte zwischen Altmühl und Rezat vorgestellt und
diskutiert. Ein besonderer Fokus liegt auf den Ergebnissen einer archäologischen Sondage nördlich des Kanalscheitels.
Neben der Sedimentstratigraphie und Chronologie wird die dendrochronologisch in das Jahr 793 datiert hölzerne
Böschungssicherung vorgestellt und konstruktiv eingeordnet. Die Bearbeitung der Bauhölzer und verschiedene dendroarchäologische Details ermöglichen abschließend die Entwicklung erster Modelle zum Bauablauf des Kanals.

In order to transfer ships, wares or persons from one water-system to another, watersheds had to be overcome. Since
the Roman Imperial period one had attempted to by-pass the respective land-routes by constructing canals. In the late
8th century the Fossa Carolina was initiated to create an artificial penetration of the main European watershed, in
order to join the early mediaeval harbour networks on the Rhine and on the Danube. As unique as this construction
is, nevertheless it does not stand in isolation. Literary sources provide manifold indications of the organisation and
process of larger, hydro-technical construction projects and demonstrate that artificial water-courses during the early Middle Ages were not rare. As far as the Karlsgraben is concerned, apart from contemporary descriptions new geoarchaeological,
geophysical and archaeological investigations allow detailed insights into the building and maintenance
of the canal. These insights will be presented and discussed for individual constructional sections between Altmühl and
Rezat. A particular focus lies on the results of an archaeological trench north of the canal’s watershed. As well as the
stratigraphy of the sediments and chronology the timber protected embankment dendrochronologically dated to the
year 793 will be presented and structurally classified. The working of the timbers and various dendroarchaeological
details finally renders possible the development of the first models of the canal’s constructional history.

Research on Early and High Mediaeval inland harbours is a challenge and a desideratum. The constructional and functional spectrum is extensive; common to all variations is their position on the highly dynamic boundary between land and water. The reconstruction of the river and riverbank development forms, therefore, a paramount part of the research into the siting and design of the harbour installations. This connection is being investigated with the help of an interdisciplinary range of methods in the two study areas of Karlburg and Salz in Lower Franconia (Bavaria). Both harbour sites are directly or indirectly joined to the River Main and were heavily affected by changes in the landscape.
In Karlburg the hitherto postulated identification of the mediaeval harbour with an »inner harbour« of the 19th century could be disproved. Instead, there is evidence of a shifting of the mediaeval riverbank opposite the modern-day bank of the Main by up to 100 m. In certain circumstances boats could have landed on this bank in the direct vicinity of the settlement. Near Salz on the River Saale in Franconia one can reconstruct from the project’s results for the Middle Ages a very pronounced terrain relief, which today has been largely levelled off by erosion and flooding. The mediaeval settlement lay on a rubble base above the high-water mark. Contrary to the Main, the Saale led to various small-scale conditions of the riverbank’s state of preservation.

Generally, the magnetic prospection is a fundamental geophysical method to reveal archaeological sites. But can the method contribute essentially and play a key role to the investigation of medieval inland harbors and settlements as well as canal structures? We enter into the question by means of the preliminary results of two interdisciplinary projects in Franconia within the framework of the SPP 1630.