Many identical pieces. Good point. But this isn't important with concrete, but they continued to build concrete arches as circular arcs. Even the pointed medieval arches are constructed from (2) circular arcs. At 10:15 AM 3/19/2012, Adam P. Goucher wrote:
Q. What do semicircular arches and viruses have in common?
A. They both comprise many copies of the same thing. The capsid (coat) of a virus is typically icosahedral or helical, containing many copies of the same proteins in a way that exploits the full automorphism group of these symmetrical shapes. Similarly, a semicircular arch can be constructed from many copies of a single stone, whereas the optimal arches (parabolae, catenaries, cycloids etc.) cannot. This should help to reduce production costs if only a single template is necessary.
We must also not forget that this symmetry gives Roman arches (and viruses, I suppose) a particular aesthetic appeal.
Sincerely,
Adam P. Goucher