The Fort (Castle) acts like a Tower when your town is under attack. Additionally, you can recruit a General who will act as a defender like Garrison but stronger.
Upgrading the Fort / Castle increases its hitpoints and damage, as well as unlocks additional Generals and/or allows you to upgrade your Generals further.
It is not possible to recruit a General while upgrading Fort / Castle.
When you deactivate a General, the cost is not refunded if you trained a second or third General with oil.
The building starts as a Castlefrom level 1 to 3, and then it becomes a Fort.
After the 5.8 balance update, the defending Generals will spawn with 70% hitpoints if the Fort (Castle) is destroyed before they go out to defend.
While Generals are in upgrade, it can be using to attack or defense once before been available.
Health of the nearby Barracks and Castle are increased by 20%. When paired with the Chapter 3 technology of Citadels from the Library and this wonder it will increase the health of your Castle by 30%.