Roads of the Roman Empire: Certainty, Density, Straight Runs and Days from Rome in the Itiner-e Network

Itiner-e is the most detailed open dataset yet of the roads of the Roman Empire: 14,769 road sections with a combined length of 299,171 km, each graded by how certain its course is. I describe the network and use it for a simple, fully stated travel-time model. Only 8,181 km (2.7%) is graded certain; 90% is conjectured and 7.4% hypothetical. A fifth of the length (19%) carries a date or the name of a builder. Treating the network as a graph of 10,315 junctions, with speeds from the middle of the ranges given in Wikipedia's article on Roman roads (22.5 km a day on foot, 45 by horse-drawn cart, 80 by courier), a slope penalty taken from the dataset's own passability field, and one day for each of four short sea crossings, London is 81 days on foot from Rome, Constantinople 75 and Alexandria, which by road must be reached round the eastern Mediterranean, 180. Carthage, 590 km from Rome, is 210 days by road, through Spain and across North Africa: a reminder that the empire's long journeys went by sea. The longest stretch of road that stays within 200 m of a straight line runs 56.1 km between Saint-Quentin and Amiens. Road density, measured in the provinces of about AD 117, is highest in Latium and Campania (144 km per 1,000 km²) and outside Italy in Cyprus, Judaea and Lycia et Pamphylia; it reflects the intensity of modern research as well as ancient road building. Interactive version: https://maps.tristanhotham.com/roman-roads/. Data and code: https://github.com/Tristan-Hotham/roman-roads. Blog post: https://blog.tristanhotham.com/2026/10/31/roman-roads/. Data: Itiner-e static version 2024 (de Soto, Pažout, Brughmans et al. 2025, https://doi.org/10.5281/zenodo.17122148), CC BY 4.0. Province outlines: Digital Atlas of the Roman Empire (DARE, Johan Åhlfeldt), CC BY. Travel speeds: English Wikipedia, 'Roman roads'. Land: Natural Earth (public domain). Derived data, figures and text: CC BY 4.0. Code: MIT.