Looking at the map currently being used in Alpha, I realized that the kingdom of Aksum was missing! Not only did the Romans know about Aksum (in Ethiopia) durring the timeframe of the game, they actively traded there out of their Egyptian holdings. Aksum was an important source of wealth to the Empire, as the Ivory harvested here was sold throughout the empire.
Granted they are less important during the early years of the game, but they were all ready well known and thriving by the end of our time frame.