The Stanford Geospatial Network Model of the Roman World
aka a Roman Empire route planner
https://orbis.stanford.edu/
Worth flicking through the About section for some commentary, maps and diagrams.
Isochrone Map of Travel Time to Rome in July
This cost distribution map illustrates favorable conditions for economic integration along the Mediterranean coast and low levels of connectivity between the Mediterranean core and the interior of the Iberian peninsula and of Gaul, the Danube basin, central Anatolia and the Egyptian deserts.