792 or 793? Charlemagne’s canal project: craft, nature and memory

Abstract

In autumn 793, Charlemagne visited the fossatum magnum (the ‘big ditch’ or canal) between the Rhine and Danube. Excavations, dendrochronology and a re‐reading of Carolingian Annals shed new light on the chronology and setting of this canal, which was planned in 792, initiated in 793, and abandoned later that year. The abandonment is attested by both written and archaeological evidence. The different versions of the annals offer a unique opportunity for comparison with the archaeological record. Evidence that works of Vitruvius circulated in the Carolingian court suggests that Charlemagne’s advisers were drawing on classical tradition when they pitched the idea of digging the canal.

Sediment budgeting of short‐term backfilling processes: The erosional collapse of a Carolingian canal construction

“…We conducted three archaeological excavations in 2013 and 2016 in the Northern and North‐Eastern sections (Figure 2), cutting the canal rectangular to the embankments (Werther and Feiner, 2014; Werther et al ., 2015, 2020; Werther, 2017). The localization of the excavation trenches was based on geoarchaeological and geophysical surveys (Linzen and Schneider, 2014; Zielhofer et al ., 2014; Köhn et al ., 2019).…”

“…Given the seasonal information of the felling date, Werther et al . (2020) could characterize the dendrochronological dates and discuss the construction progress at high chronological resolution. Besides the chronological information, the timbers might have marks of decay (unless they were stored in anaerobic conditions, which stops further decay) (Schweingruber, 1988).…”

“…At the Fossa Carolina, it divides the Altmühl catchment (Danube drainage system) from the Swabian Rezat catchment (Rhine–Main drainage system). According to historical sources, the Fossa Carolina was built in AD 792/793 on a valley watershed (Figure 1) and according to the revised version of the Royal Frankish Annals its termination ought to have been caused, among other things, by heavy rainfall, which induced intense erosional processes of the construction earthwork (Hack, 2014; Nelson, 2015; Werther et al ., 2020). ‘For because of the continual rain and the bogginess of the land which was in the nature of things completely waterlogged, the work that was being done could not hold firm, given the excessive wetness, and as much of the earth as was excavated by the diggers during the day slid back again and sank into the soil during the night’ (translation of the revised version to the year 793, after Nelson, 2015).…”

“…Therefore, in this study, we present stratigraphic and geochemical results to identify these backfills. Three archaeological excavations in the Northern and North‐Eastern Sections have revealed the status of construction at the moment of abandonment (Werther and Feiner, 2014; Werther et al ., 2015) and several oak timbers were recovered (Werther et al ., 2020). Furthermore, we compile the radiocarbon ages of the backfills, and we determine the spatial distribution of dendrochronological data from the Early Medieval canal construction.…”

Collaboratory, Coronavirus and the Colonial Countryside

“…Another new and significant study relating to early medieval engineering has ramifications for understanding linear earthworks. Werther et al (2020) explore the archaeological and historical evidence for Charlemagne's failed attempt at building a canal ('big ditch') linking the Rhine and Danube, arguing that this hydraulic work was inspired by the writings of Vitruvius. They report on archaeological investigations which reveal from dendrochronological dating that the canal was commissioned in AD792 with work beginning in the spring of AD793 and abandoned later that same year.…”