First introduced with Rival Domains on March 8, 2018, fortresses grant any unit occupying them a damage reduction of 30% of their Def or Res and restores 10 health to the unit. If the fortress is colored blue, the fortress is controlled by the player, and if the fortress is colored red, the fortress is controlled by the enemy.
The fortress is given three health and will be destroyed by the opposing force if the fortress is reduced to zero health. When destroyed, the battle ends and the player is shown their results.
When either team loses a unit, the next unit will respawn at their respective fortress and the sigils adjacent to the fortress. In Relay Defenses, only three units can respawn at their fortress and adjacent sigils, and the other two respawn at their camps.
Unlike defensive terrain, fortresses cannot be combined with trees or trenches.