On the roads and rivers of Late Iron Age Gaul: Adjusting least-cost path analysis to multiple means of transport and imprecise data

Abstract

Celtic societies at the end of the last millennium BCE experienced a shift in the scale of production and exchange, leading to a revolution in mobility.

This study aims to investigate these ancient exchanges by focusing on their primary constraint: the difficulties of transportation. We seek to estimate the remoteness between sites from a merchant's perspective, considering transport costs, that is, the challenges of moving heavy and bulky goods over long distances.

Our approach is based on Least-Cost Path (LCP) estimation, which we adapt to address the various complexities inherent in applying this method to ancient transportation systems. These complexities include the multimodal nature of transportation, involving inland transport, upstream and downstream fluvial navigation, and the lack of or imprecise nature of data regarding navigable sections and transportation costs. While LCPs are widely used in archaeological contexts, a standardised methodology for calibrating them and selecting algorithmic variants remains elusive, particularly when reference paths are absent.

This article offers firstly a methodological contribution to the development and rational application of LCPs in archaeology, adapting them to the limitations of our data and the multimodal nature of goods transportation; and secondly an archaeological contribution demonstrating the crucial role of considering the constraints of ancient mobility in exploring the evolution of past societies' territories.