These are towns. The citizens have grown lax under the AI peace, and cut the budgets to garrisons. Now that foreign invaders (ie us) have come, they are unprepared. The silly city folk have spent all their money on silks and furs, lavish parties and useless ornamentation. The true soldiers, having been laid off, retired to the castles where they practiced their martial culture whilst the townsfolk danced and frolicked. But now the time of reckoning has come. With no paid garrison, the citizen-soldier must don their heaviest garments and take up their dusty unaccustomed weapons and attempt to defend their AI traditions. But times are different now. The barbaric blood lusting hordes from North America and Europe (with the odd Brazilian thrown in (yeah Ogerp, put you in the mix)) have entered Calradia, and now their civilized, peaceful way of life will be crushed, and every man woman and child will be slaughtered in true, modern, developed civilization style.
So, in a nutshell, castles strong, cities weak.