After reaver raids by the Stygian Empire, or when retaking territory from the Stygian Empire, Imperial forces encountered cairns and bone piles. These were sometimes just acts of terror to demoralize Imperial forces. Sometimes they were psychicly attuned traps that warped the minds of those who ventured to near and turned the weak of faith towards the dark gods of chaos. Other times they were attempts to draw forth the eye of the dark Pantheon. Sadly for the Imperium they would be a frequent sight during the Stygian Wars.