As macro-shape we understand the general three dimensional morphology and geometry of the stereotomic construction. For example, Romans used almost exclusively the circular segment as a generator curve for arches, barrel vaults and their intersecting shapes.
The nature of this macro-shape is influenced mainly by two factors: a pre-conception shape and the requirements for static stability. The perfection of the geometry implicit in a round arch, with all its points at the same distance of its center is too powerful in its analogies with the observable round forms in nature. It is only understandable that the first practitioners or arch structures saw in the half circle the human abstraction capability to interpret arch structures in nature. As such, for centuries this shape was the only used, adapted only by regulating its thickness or abutments.
The exploration of architecture shapes and structure functioning throughout history allowed for other curves to be explored and adopted.