Monasteries mainly serve as a Monk production building. As Monks are important for supporting and healing troops players will normally build at least two Monasteries for that purpose. If the player is intending to use their Monks for offensive purposes like a Mush (Monk rush) they must have at least three (preferably four) Monasteries since the production of Monks is slow and the unit itself has slow movement. Also, technologies must be researched at the same time, first of all Sanctity and Fervor.