The
universe of the Mongols can be visualized as a circle, not only in the
three dimensions of space, but also in time. Everything has a circular
motion: the path of the sun from day to day, the cycle of time from year
to year, and the cycle of the spirits of all living beings that return
to the earth to live again and again.
Intersecting the circle are the axes of the four directions and the axis
of the center of the world, going up to the upper world beyond the
eternal heavens and going down beyond mother earth to the lower world (http://www.newworldencyclopedia.org/entry/tengriism)