For all the grain of ... Africa
This comes up again and again in Gibbon's history. I shake my head every time. What? Really? You can't grow wheat in Italy? This seems completely counter-intuitive. I thought you could grow wheat almost anywhere.
Well, during the African war, about 400, in the days of the Roman General Stilicho, they hit on a brilliant solution to replace the grain from Africa: import it from Gaul. Float it down the Rhone to the Mediterranean, then down the coast to the Tyber. Which, of course, will work only until there's trouble in Gaul. And it seems you never have to wait long for that.