Civilizational collapse is a hell of a drug. Also, the fact that political and cultural power was centered in the cities meant they were looking for solutions to very similar problems in very similar ways to the problems we have now. You get a lot of very familiar looking thinking that way - questions of legalism, markets, public infrastructure, compromises between public safety and private freedom, accommodating unregulated individual behavior, ensuring peace between total strangers, etc!

After the collapse of the (Western) Roman Empire, political and cultural power would be overwhelmingly invested in rural magnates, and that wouldn't really finish reversing back to urban primacy (at least in Europe) until the 19th century AD.