Geoarchaeological prospection for Roman waterworks near the late Holocene Rhine-Waal delta bifurcation, the Netherlands

Romans who settled in the Low Countries at the northern margin of their empire were practicing diverse systems of water management to maintain economic and above all strategic stability. In the early Roman period (12BC–AD 70) they created a shipping route from the Rhine towards the north by digging canals and constructing dams, such as the Dam of Drusus, accompanied by the adjacent Roman fortress of Carvium (Herwen). This dam was situated at the bifurcation point of the Rhine and Waal river branches and was designed to channel more water into the Rhine. All these engineering feats were undertaken in order to control the northern part of Germania via the Wadden Sea and the German rivers Ems, Weser and Elbe. By the middle Roman period (AD 70–270) the Romans had cancelled their efforts to subdue Germania and this is a period when the Rhine is known as the limes (Roman state border).  The research area described in this paper is situated near Herwen in the eastern part of the Rhine–Meuse delta system. The area has a dynamic late Holocene erosional and depositional history, close to the river system's equilibrium point. In order to reconstruct the former landscape and to investigate whether evidence of Roman waterworks could be detected, geoarchaeological coring campaigns were carried out to gain insight into the sedimentology, chronology, stratigraphy and geoarchaeology of the region.  Results indicate that Pleistocene sediments are only preserved in the western part of the research area, but further east then previously known. Dating of gullies and levees has confirmed Roman and potentially pre-Roman fluvial activity closer to the Roman fortress of Carvium then was previously known. Four newly discovered residual gullies provide a greater insight into the character of the Roman landscape than hitherto known.  The largest of the newly identified gullies may be instrumental in finding the location of the Dam of Drusus, however, much depends on the question as to whether the gully represents an actual former stream channel or simply a crevasse and this cannot be ascertained on the current evidence. Nevertheless the results of this study reinforce the assumption that the Roman castellum was situated on the apex of the Insula Batavorum and close to the Dam of Drusus at the bifurcation of the Rhine and Waal