The southern base is put in place. Note the saddle carved out for the springer.
In my first year of college I majored in architecture. Although I ultimately decided I did not want to be an architect, nevertheless I retained a lifelong interest in certain architectural principles, particularly the fundamental discoveries of the classical period. And chief among them was the principle of the arch. I was fascinated with how pieces of stone fashioned to fit together in a certain way--such that if one piece is missing, or until all the pieces are in place, there is no structure--when complete can support an almost infinite amount of weight. And in so doing, they form not only an engineering marvel, but also, based on the eternal circle, a thing of beauty.