Wowww, the Stanford Geospatial Network Model of the Roman World is really fucking cool. It's an interactive map that gives you a sense of the flow and time to travel of information/goods between different geographical points in the empire during different seasons and by different modes. Basically there are counterintuitive flows to a modern eye because, for example, crossing a mountain in the winter was an enormous task in a way it is not now.

orbis.stanford.edu/