Comments on the 300 AD scenario:
1) Japan starts with only 2 fishing boats. I guess the civ must have already spawned by then.
2) Maybe some starting culture for the cities?
3) And maybe more cities? Especially for the Roman Empire. Dyrrachium? Mediolanum? For Persia, Spahan can already be placed there.
4) Should Orthodoxy already be founded in Jerusalem at the start? This assumes that the founding date is shortly after Jesus' death (Paul's missions?).
1) Fixed
2) Although you are technically right, I don't consider it a major issue. Let's say that civilizations expirienced some severe crisis.
3) Wow, to be honest I expected exactly the opposite reception on Rome, that it has too many cities. Anyway, I added Milan, Sigidun and Shush. Spahan will spawn with Sekjuks