The Worldstone, otherwise known as the "Eye of Anu", "Heart of Creation" and "Heart of the World" was a colossal, mountain-sized object of immense power. Sought by both angels and demons, it would be used to create Sanctuary before being destroyed as a result of the Great Conflict. And yet for all its importance, few of Sanctuary's inhabitants are aware that it even existed.
The Worldstone originally lay in the realm of Pandemonium, the scar of the universe's violent birth from the battle between Anu and Tathamet. It was the foundation of all places and times, a nexus of realities. A foundation that the forces of Heaven and Hell sought control of. Oral history states that whichever side controlled the stone allowed it to alter reality and create life and worlds with barely any restriction. Both angels and demons created worlds that reflected their nature, but all of these worlds were inherently flawed, and were doomed to wither and die. At some point, the archangel Tyrael ordered that a bastion be built around the stone, which would come to be known as the Pandemonium Fortress. The fortress changed hands many times over the course of the Great Conflict, and the possession of the Worldstone alternated in turn.