Pandemonium is the center of creation and the location where the Heart of Creation, more commonly known as the Worldstone or the Eye of Anu, existed prior to being stolen by Inarius and Lilith. This was the place where Anu and Tathamet finally obliterated each other and created the known universe.[1]
This realm was the main battleground between the forces of Heaven and Hell before the creation of Sanctuary, when the conflict still remained wholly focused on obtaining control over the Worldstone.[2] At one point when Heaven held control over the stone, Tyrael ordered the construction of the Pandemonium Fortress around the Worldstone.[3]