Barracks are a mandatory building in the game. It is the only way to train troops besides buying them at the bank offers with real money. You must have at least one barracks you can't demolish, and can build any number you want, up to 12, on the western bank of your Town.
Each upgrade level of the barracks adds to your troop training capacity. It does not provides any other kind of bonus like boosting the training speed. Therefore, it is strongly advised to have the lowest possible number of barracks in your town (1-2), manors and infirmaries providing much more useful support : training speed and heal capacity.
It is recommended to have barracks train warriors all the time.
Requirements: You can only upgrade a barrack if you have at least one Stone Quarry and Forge already upgraded to the same level as you are trying to upgrade to. Example; If you want to upgrade a Barrack to level 14 then you must have at least one Stone Quarry and at least one Forge that is upgraded to level 14 or more.