Tavern is a building which sets the maximum possible number of spies you can have. Taverns are required for an espionage. Taverns can only be built at the main castle in The Great Empire, and the maximum number of buildings is 3, making the maximum possible agent number 39, or 44 with research. The number of agents can be further expanded in the research tower. If the espionage is not successful the target will get notified of who attempted to spy on them.