Quite. Also, walls cost 2 manpower of the culture the city is. So walls on a Macedonian city cost 2 Macedonian manpower, and walls on a non-Macedonian city cost 2 mercenary manpower. I don't think the game ever lays it out for you but they posted it on their forums and it's true in game. So if you need more phalangites just go Mr. Gorbachev all over the place. Cities without walls will never rebel, regardless of the culture.