Her is a map you could use for a Late Antiquity RP. 

[img]http://i.imgur.com/sqKYYkZ.png[/img]

I mostly decided to include people who would be important to the politics of the Romans, Persians, or Arabs. Most of what is blacked out is tribal land too far from the area of the RP. I'm assuming the Ostrogoths would have disappeared/been swallowed by the other groups, and that the Vandals would have been kicked out since Africa is the breadbasket of Italy, and since it was taken out by the Byzantines in the real world 6th century anyway. I mashed a few Dioceses together so the Roman Empire isn't too divided. An Emperor in Constantinople and a Co-Emperor in Rome fits with late-Roman tradition.