It is often said that Egypt became the breadbasket of the Roman Empire, with Egyptian grain shipments being vital to support the "grain dole" for the poor of Rome.

But I'm having a hard time picturing the actual mechanics of it.

How was the grain shipped? Did they have specialized ships for shipping grain? How did they manage to keep all this food from spoiling? Was it just grain or was other food also moved around the Empire? (Aside from the famous Spanish olive oil)

I would appreciate if you could point me to some reading on this.

Thanks!