On a only loosely related note, as a historian, my greatest dream would be to find evidence of the existance of precisely a single Gaul village that the romans never managed to conquer. But I get ahead of myself.
In all seriousness, the Gaul should totally have some bonus benefiting their priests, to referr to the influence that druids had on their society. One idea I had would be for priests to cost wood instead of gold, what sounds pretty useless until you remember the teensy, tiny detail that gold is usually the first resource to run out on these matches.
Oh, the Scythians! I know very little about then, but I like then! I just think we would need to remember not making then feel too much like the Egyptians. My idea would be for then to have better "conventional" cavalry forces but lack the "unconventional" ones, aside from their Chariots. What I mean is: Remove the elephants and the Camel Riders, tack in Cavalry, Heavy Cavalry, and Horse Archers. Since-All-Scythian cavalry was good, not just their Chariots, another bonus they could have is free Nobility upon building a Government Center, on top of a faster attack rate for their Chariots.
For the Huns: We would just need a different bonus for then, to set then apart from both the Yamato and the Scythians. One idea I had was the ability to train Horse Archers on the Bronze Age( Though they would still need to wait for the Iron Age to train Heavy Horse archers ), but I am not sure if that would be overpowered... Or, fudge, we could give then the Chariot Archer and let their bonuses be focused on the Horse Archer and cavalry-line anyway. No rule saiyng we cant
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