The Roman arch prevented rigidity solely, maintaining each of the masonry in compression, through the keystone on the piers. Stone in compression has good toughness, and also the Romans developed enormous arched bridges and aqueducts in massive figures. Extending their arch into a tunnel, they invented the barrel vault, with https://objects-us-east-1.dream.io/blissdrive/westhillmasonry/Hardscape-Contractors.html