Network science reveals the structure and lasting impact of the Roman road system.

Ancient infrastructure can leave lasting imprints on modern settlement patterns and mobility. The Roman road network connected vast regions of Europe, North Africa, and the Middle East, and is often mentioned as an example of such long-term impact. Yet its structural characteristics remain largely unquantified. Here we present a high spatial resolution quantitative exploratory analysis of the Roman Empire's road system, enabled by our creation of a spatially detailed Empire-wide dataset. We address long-standing questions concerning the straightness and persistence of these roads, and the centrality of cities like Rome. We show that Roman roads tend to be straight where topography allows but less so than modern roads; provincial capitals were more centrally located than other cities for mediating terrestrial mobility; segments hypothesised to be main roads were more important intermediaries than secondary roads; and Roman road density correlates with major modern roads.