We just really don't know very much about the roman economy, and are unlikely to find out much more than we currently do.

On the other hand we do know a lot about what happened in 1921, Krugman just wishes we didn't because it appears to contradict his theories.

Generalizing from one example isn't good .. science, logic or argument. But it's better than generalizing from the fog of history.

Um, no. History contains evidence, it's not particularly clean evidence, but evidence nonetheless and we shouldn't be throwing it away.