Fortress World

A Fortress World is a type of planet within the Imperium of Man that serves as a bastion of the Imperium's defence against some constant and persistent threat to Imperial space. These worlds are extremely well-defended, usually with large numbers of Imperial Guard regiments and Imperial Navy assets, and their populations and economies are wholly geared towards meeting the demands of Imperial defence. Unfortunately, not all Fortress Worlds are controlled by the Imperium, as several have fallen to the control of the Traitor Legions. The most famous Fortress World in the Imperium is Cadia, which defends the Cadian Gate, the only stable passage through the Warp from the Eye of Terror into open Imperial space, from the constant assaults of the Forces of Chaos and Abaddon the Despoiler's Black Crusades.