Unholy Legion is a Warriors of Chaos settlement building in Total War: Warhammer. When the omens are strong, the Unholy Legion converges.
The legions of Chaos yearn for souls with which to feed their Dark Gods. When a champion stands forth, worthy and powerful enough to command the might of its legions, they will cease infighting and prepare to march south. For that is where the harvest is: the souls required to slake the Chaos Gods' thirst.