As the water flows: A method for assessing river navigability in the past

Abstract

Although textual and archaeological sources inform us about the importance of river transport in Protohistory, Antiquity, and the Middle Ages, integrating it into studies of ancient mobility remains a challenge. Empirical navigability studies are time-consuming and are only feasible for rivers well-documented by historical, archaeological, and palaeogeographical studies.

This work proposes a method for realistically approximating navigable sections without empirical data by algorithmically detecting the plain sections of a river and testing its reliability as an indicator of navigability. Using 18 rivers in central-eastern Gaul, for which we have empirical knowledge of ancient navigable sections, we demonstrate that estimating the plain section of the river based on a change-point detection algorithm provides a good approximation of navigable sections. This method is applied to 48 Roman rivers where empirical information about navigable sections is scattered. A subset of these rivers is then empirically tested to validate the results obtained.

Applying this method offers a new perspective on navigable areas in the Roman world, providing a reasonable first guess that could guide future empirical research into the navigability of ancient rivers.