Treason's Final Reward

Treason's Final Reward is an found in the Paths of the Drowned in  of Diablo III.

In their journeys, the Nephalem may encounter a pit with the Pillar of the Faithless in its center. Touching the pillar will unleash a swarm of Skeletons and Skeletal Archers led by Magnar. Killing them all ends the event, rewarding experience and gold.

Apparently, the pillar served as a prison of sorts for the souls of those who betrayed Rakkis.