The Fortification of Gaul and the "Crisis of the 3rd Century"

[Nathan Ross]

the effort that the central state mustered to fortify Gaul against the barbarian tide... proved that Gaul was still very much prospering in the 3rd-4th centuries AD.

It's interesting that the scale of the effort indicates that Gaul was worth defending, but also that the threat was real!

What evidence do we have that Gaul was not prospering though? The agri deserti in northern Belgica were real enough, although in places the problem seems to date from the later 2nd century, and perhaps relates to land impoverished by over-farming, and/or turned over to sheep pasturing, rather than barbarian devastation. Diocletian's prices edict mentions wool from the Atrebatic and Nervian lands.

Nico Roymans' Villa Landscapes in the Roman North: Economy, Culture and Lifestyles (2011) suggests that even in the north of Belgica many larger villas continued in operation, particularly along the fertile loess soil belt between Koln and Bavay. The movement of the imperial court to Trier stimulated a lot of new development in the Moselle valley as well, which suggests that this area was not considered a dangerous frontier zone at the time.

While many of the fortified cities contracted to a much smaller plan, that does not necessarily mean that they were poorer or less prosperous. Besides, several of these fortifications turn out to date from the mid 4th century, rather than the mid 3rd.