Functional building are necessary to be able to hire mercenaries and build an army. They are also needed for different other things like for example to train your mercenaries, to execute unwanted mercenaries, to build an alliance and much more

MercbarrackSquareMercenary Barracks RecruitChamberSquareRecruitment Chamber HiringQsquareHiring Quarters
TrainingChamSquareTraining Chambers PPsquarePigeon Post CataSquareCatapult
THsquareTusk Horn CPsquareCity Planner ExeSquareExecutional Guillotine
CHsquareCentral Hiring BeastCaveSquareBeast Cave BeasKeepSquareBeast Keeper
HoBSquareHouse of Brotherhood AllybarrackSquareAlliance Barracks BlacksmithSQuareBlacksmith