The Fortress is the heart of your City. Monitor your resource production and adjust the tax rate here.
You start out with a level 1 Fortress already built. The look of your level 11 Fortress depends on the Race of the character. You can change your race by using a Tribal Rebirth.
The level of your Fortress determines the number of fields you can build, as well as how many wildernesses you can control at that time. This information is shown by clicking on the Fortress.
Once your fortress is lvl 11 you can start upgrading your all other buildings to level 11 and above.
Requirement to Upgrade and Power Boost
Note: The power boost received from the Fortress is the same as you would receive from the Wall or the Dragon Keep. The power you receive is cumulative. The total power that you can receive is therefore 51,200.
When you click on the Fortress, you will see this screen. At the top, it tells you the usual information about the building. The blue text tells what you are currently able to have. The white text tells you what the benefits of the next level are.
At the bottom, it tells you what your resource production rates are, and the boosts you are currently receiving from wildernesses and Nanos' usage.