Via IO9, I learned of a new interactive map of the Roman world: ORBIS: The Stanford Geospatial Network Model of the Roman World.
You can set a starting and destination point (say Jerusalem and Tarsus, for instance), and find out what was involved in traveling between the two by various means of transportation, including what provisions would be needed and other such details we may neglect to think about.
Click through to take a look and explore its features. Here’s a video about how it works:
It seems to not work on Chrome, but was impressive on Internet Explorer.