The first sketch shows my initial conception of the Pillar of Heaven which had a small lake set into its summit. This lake fed a series of waterfalls that cascaded down the Pillar in what later became the Rainbow Stair. At this point I conceived of the Halls of Thunder as being built into the cliffs overlooking this lake. Both these and the summit lake were discarded.
The final form the Pillar took is shown in the second diagram – which can also be seen in the model I made of Osrakum. It is based on Devils Tower in Wyoming – which incidentally was the mountain which plays a central role in Close Encounters of the Third Kind.
The Pillar of Heaven dominates the heart of Osrakum. Close to its summit it has been hollowed to form the caves and chambers known as the Halls of Thunder. It is here that the God Emperor and the rest of the House of the Masks retire from the summer heat. In this respect, the Halls of Thunder perform the same function for the Imperial House as do the various eyries of the other Houses of the Chosen. The Halls of Thunder are reached from the Labyrinth by means of the Rainbow Stair.