A technique for modelling networks with junctions and what it tells us about the Roman road network of Gaul

Abstract

Many different techniques have been applied for the construction of putative networks to model connectivity and communication between ancient settlements. The large majority of these networks consist of edges joining at settlement nodes, without representing the fact that real road systems have junctions and crossroads at locations away from settlements. Here it is shown that the minimum total cost principle of network generation, based on optimising the balance of build and travel cost, can be extended to generate junctions and crossroads. This further improves the cost-benefit ratio by reducing road length for little penalty to the traveller. The resulting junctions divide into two main groups – perpendicular and oblique – with angular separation increasing and relative frequency changing as network complexity increases. Analysis of the population of junction angles in the Roman road network in Gaul suggests strong similarity to theoretical networks with a travel-to-build cost ratio of 7, similar to that found by a different technique in an earlier study, encouraging some credence that the network construction methodology approximates actual practice. The angle distribution further suggests a model based on local networks built around pre-existing through-roads.