I guess I was pretty vague, sorry. There will be a small number of slaves, traveling from Thebes to Rome. I am trying to track down some details to make the journey as authentic as possible.
I put some more details in the above reply.
Ok, I would say that a guardian of some kind, probably a freedman to the owner (and perhaps one or two guards) would take a ship from Greece to Rome. Whats important to remember here is that sailing was nothing like taking a ferry today. It was much more like hitchhiking on the sea, you took one ship that would get you closer to your destination, no matter where it sailed, then take another and another again.
You will find a good example of this in the bible actually (Acts of the Apostles 27-28).