Quote Originally Posted by ranpiz
on the campaign map it seems that the AI cannot deal with huge unit sizes.

it will deplete the population of virtually all of its cities down to 400
This is an issue on normal unit size for most of the barbarian cities as well. Only Patavia, Alesia and Corduba are definitely immune, though it's possible Londinium can also be added to that list.

I have seriously considered switching to small units to reduce this problem and to decrease pathfinding problems during city assaults. That I haven't done so is because I think combat will throw up some very strange results and because I am concerned that the city garrison effect will not scale with unit size, an effect that would make playing with small units impossible.