A post at a blog called A Fine Theorem contains an interesting nugget:

The Romans famously conquered Gaul – today’s France – under Caesar, and Britain in stages up through Hadrian. Roman cities popped up across these regions, until the 5th century invasions wiped out Roman control. In Britain, for all practical purposes the entire economic network faded away: cities hollowed out, trade came to a stop, and imports from outside Britain and Roman coin are near nonexistent in the archaeological record for the next century and a half. In France, the network was not so cleanly broken, with Christian bishoprics rising in many of the old Roman towns.

Here is the amazing fact: today, 16 of France’s 20 largest cities are located on or near a Roman town, while only 2 of Britain’s 20 largest are. This difference existed even back in the Middle Ages. So who cares? Well, Britain’s cities in the Middle Ages are two and a half times more likely to have coastal access than France’s cities, so that in 1700, when sea trade was hugely important, 56% of urban French lived in towns with sea access while 87% of urban Brits did. This is even though, in both countries, cities with sea access grew faster and huge sums of money were put into building artificial canals. Even at a very local level, the France/Britain distinction holds: when Roman cities were within 25km of the ocean or a navigable river, they tended not to move in France, while in Britain they tended to reappear nearer to the water. The fundamental factor for the shift in both places was that developments in shipbuilding in the early middle ages made the sea much more suitable for trade and military transport than the famous Roman Roads which previously played that role.

This prompted an interesting comparison from Steve Sailer:

Maybe this is analogous to the recent shift from landline telephone networks to wireless telephone networks. Landline networks, like Roman roads, required a lot of social organizational capital to build and maintain, as Americans had in the AT&T era, but many other countries did not. Lots of cultures, such as the 20th Century Italians, had a hard time maintaining a landline system.

In contrast, cell phone networks don’t require a society to be good at cooperating, so even anarchic Somalia can have decent cell phone service. You just have to have a few people who knew what they are doing.

Similarly, medieval shipping networks required concentrations of technically advanced shipwrights here and there, but didn’t require a giant Roman-like state to keep the roads repaired. The ocean repairs itself.

It is striking how land-oriented Roman culture was despite emerging on the Italian peninsula where no place is very far from the sea, the land is mountainous, and the sea is relatively calm and warm. In contrast, England has fairly mild terrain and the Atlantic ocean is more tumultuous than the Mediterranean sea.

Maybe the explanation is that British rivers were better for transport than Italian rivers south of the Po due to more rain and less severe slopes, so it was easier to get started with inland shipping and then continue out into the ocean as your technique improved. But Italian rivers tended to be short and steep and go dry now and then, so they weren’t as good launching pads for eventual saltwater navigation.

Maybe, but Venice and Genoa did dominate maritime trade on the Mediterranean in the high and late Middle Ages…

For my part I am interested in how little influence the Roman Empire ultimately had on Britannia, certainly when compared to Gaul. I assume this is one reason why French is a Romance language while English is a Germanic one.