The Roman arch prevented rigidity completely, keeping all of the masonry in compression, in the keystone to the piers. Stone in compression has terrific toughness, as well as Romans created large arched bridges and aqueducts in large quantities. Extending their arch into a tunnel, they invented the barrel vault, with https://vymaps.com/US/West-Hills-Masonry-VN23008/?id_new=91f028d46d98c5b158f38e36720f8a1f