But also the technique of leavening using natural yeast has been known for thousands of years; it pre-dates the Romans, who definitely used it in their regular

But also the technique of leavening using natural yeast has been known for thousands of years; it pre-dates the Romans, who definitely used it in their regular bread. I'd say that running a bakery under those conditions: i.e. would always be yeast around and there is no refrigeration, so for any given dough it's a question of when, not if, a given piece of dough will start to rise.