-The barbarians can only build primitive roads anyway.
-Knowledge of Siege equiptment was not exclusive to the Romans or the 'civilised' parts of the world. The advantage the Romans and civilised peoples had was their knowledge of mathematics which allowed them to build more accurately and also to fire more accurately.
-The AI already simulates a poor team effort very well. The game would be a complete walkover if it were mostly rebs out there.
-Elephants, cant argue with that.
-I haven't played with chariots much so i wouldn't know
-Bull, they had ship building technology of their own. An AI tweek so that they don't spam them would be good though.