What is it about the figure of the ring, the circle, that so attracts humans? There is something innately satisfying about it. In music we often return to the opening theme in order to finish up. And in poetry a reference to it can fill our hearts with longing, as in this from Little Gidding

We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.

Great piece. It sent my brain spinning away.