Usually it is the Brigands who disrupt trade, and the Brigands are the ones I see on the roads. It is my understanding that if it is not Brigands, say the Iceni Rebels in Britannia, they will not disrupt trade. Correct me if I am wrong, anyone. Those Halicarnassus rebels off the road might not be Brigands, but instead Lydian Rebels or something like that. I have noticed rebels like to pop up between Ariminium (or Arretium, I get the two confused) and Tarentum, and again just north of Ariminium (or Arretium, whichever one is to the east). Those usually have mercenary Hastati.