Iron provides production to the city that works it. It is required for the production of many military units and doubles the production speed of the Eiffel Tower.
When early civilizations began to use metal to construct tools and weapons, the most commonly used metal was bronze. Bronze had the advantage of being readily available and easy to work with. Unfortunately, it was too soft to hold an effective edge. In the mid-14th century BC in central Europe, iron replaced bronze as the metal of choice, and the Iron Age was begun. Since this time, iron has been a valuable commodity. Deposits of iron and iron ore found in mountains are mined and processed for use in their raw form, and in the production of steel.