I have a mini theory (and that's all it is)..

If you notice, the ai will move it's capital around as if it meant nothing. I was playing a Baktria game with FOW off, just so I could actually see everything that was going on in the West. Rome moved North, West, East and South, and looked like an unstoppable Juggernaut. They had taken All of Italy, most of Gaul (all the way up to the English Channel), East across almost to Hungary.

Carthage held on in Lilybaum, and suddenly started turning first Sicily, and then Southern Italy white. And while this was going on, I noticed that the Roman capital was now Viennos. They didn't seem to care that their Italian homelands were being rampaged. Then Rome was finally carted out of Italy, and of course with no "real" factional troops left, the Getai and Sweboz started to pick away at their provinces too.

It was the complete empathy, that the ai Rome seemed to show about Carthage rampaging through Italy that bemused me. And it's not the first time I've seen this.

So the mini theory, is maybe there is some hidden weighting somewhere, that causes the ai to give more value to defending the territory around it's capital, even when it's capital is somewhere completely unimportant, because it's moved it around.

Just an out there theory ;)