Metal represents all metals and construction materials used for
practical purposes, such as construction and armaments. It is found
in metal mines. The production of each mine is greater if the sector
has a higher metal parameter, and is also increased by your nation's
mining skill. Your mining skill can increase if you invest in
technology, because your nation will discover better tools for mining
and prospecting.
You can spend your metal in several ways, including drafting armies,
technological R&D, constructing fortification and roads...