The district buildings can store other building inside them. This is giving you more space on your castles and outposts for decoration items, which increase your public order. There are 3 buildings: "Military", "Trade" and "inner" districts each can hold different buildings, but all have the same upgrade plan. As higher you upgrade a district the more building it can store. You may read further about district buildings.
|Level||Construction tokens||Upgrade tokens||Space for buildings|