Very interesting, however it paints a misleading picture of the empire because it is missing the most important trade and shipping routes: over the sea.
I always found it incredible how Rome, a city of angry shepherds without a real port and with no serious tradition of seafaring, ended up using the whole of the Mediterranean as its personal highway and the heart of a huge Empire.
In fact, they did the exact opposite, at least initially. Pretty soon they were up against Carthage, a huge naval power with a long tradition of seafaring inherited from its Phoenician roots, and were soundly beaten in the first few engagements. The Romans turned it around by changing the game: they developed "boarding" tech that would basically switched naval engagements into more traditional brawls -- what caribbean pirates were still doing almost 2000 years later.
In the long run, of course they acquired real sea skills; but they only leveraged those skills after they had acquired total domination over the Western Med. That's just amazing, imho.
