When a Celestial Pillar takes control of a map area in Terraria, it changes the background to a pillar-specific one and spawns only pillar-specific enemies in large numbers. The pillar itself is completely stationary, apart from slowly bobbing up and down in place. Each pillar controls a circular area around it with a radius of 250 tiles or 500 feet. The area reverts back to normal once the Celestial Pillar is defeated, which requires killing a certain number of its spawned enemies to remove its protective shield.