Roads and rivers. The importance of regional transportation networks for early urbanization in central Italy (950-500 BC)

Ancient regional routes structured interaction among settlements and shaped the emergence of complex societies. We apply a network framework to central Italy (ca. 1000–500 BC) that compares a terrestrial-only baseline with a dual-mode system adding river routes, using a connectivity metric that reflects resilience (availability of alternative paths) while accounting for cumulative maintenance costs. Rather than simulating traffic, we explore ranges of relative costs for river upkeep and for port maintenance required to switch between modes. Wherever, within these ranges, the dual system connects settlements more robustly than roads alone, we say it outperforms the terrestrial layer; the broader the set of plausible cost regimes meeting this condition, the stronger the functional interplay between modes. In this application, the terrestrial network of Southern Etruria appears less resilient than that of Latium vetus, and the compensatory role of rivers there was constrained by the scarcity and fragmentation of navigable waterways; in Latium, river routes more often reinforced regional connectivity. More broadly, the framework is transferable to other settings where multiple transport modes coexisted and required maintenance (e.g., roads with canals or managed rivers), enabling a grounded assessment of how intermodal choices shaped the efficiency and resilience of past mobility systems.