When a mine is built, players are grated a small bonus of 25 metal, in addition to what they harvest. A mine may only be placed on an unoccupied mountain or cliff and the size of the mountain and cliff determines the amount of workers the camp can hold. Some civilizations have national powers that grant them bonuses to their metal production.
Metal is used throughout the entire game to produce units, research technology, and build structures. Metal is used mainly in the production of siege, artillery, and late-game sea-based units. It is also used in the creation of buildings and is needed for technology upgrades.
Obtaining metal is considerably difficult as there are limited numbers of mountains in a map. Furthermore, there can only be one or two mines occupying a mountain. While it may seem that metal is abundant for a time, building up an army will greatly increase the demand for that resource.