The Mill is an Economic Building where most of your nation's Food is stored. Multiple Mills may be built, with your Food split evenly among them. In addition to storing Food, a player can trade Metal for a Food Shipment there.
When you have enough Metal to order a Food Shipment, the text "Trade available" will float up from the Mill.
The shipment size and the required number of Metal increases with the level of your highest level Mill.
Attacking players can loot up to 25% of the stored Food in your Mills.