What created the Tower?
The Wheel created it. The Wheel is the structure of this universe, and it is easiest to see it that way: rim, spokes, hub, and all the spaces within and without. I shall take each in turn.
What created the Wheel?
Anu and Padhome, stasis and change, both vast realms sitting in the void, they created it. Not vast, infinite, as the void was infinite. Imagine an infinity enclosed by another; you come away with a bubble. Now watch as the two bubbles touch. Their intersection is a perfect circle of pattern and possibility that we shall call the Aurbis. The Aurbis is the foundation of the Wheel.
What are the spaces within and without of the Wheel?
Outside the wheel is the void, bereft of anything. It cannot be named. If it has more aspects than stasis and change, they are outside of true language. Inside of the Wheel is the Aurbis, as I have explained.
What is the rim of the Wheel?
As the process of subcreation continued, both Anu and Padhome awakened. For to see your antithesis is to finally awaken. Each gave birth to their souls, Auriel and Sithis, and these souls regarded the Aurbis each in their own part, and from this came the etada, the original patterns. These etada eventually congealed.
What is the hub of the Wheel?
We are the hub, the Mundus that goes by many names. We are the heart of all creation. What does this mean? Why should we care? Lorkhan created it so that we could find what he did. In fact, and here is the secret: the hub is the reflection of its creators, the circle within the circle, only the border to ours is so much easier to see. Stand in its flux and remain whole of mind. Look at it sideways and see the āIā.
This is the Tower.
Hope that helps. Wheels are kind of complicated in TES.