Longstanding Design: Roman Engineering of Aqueduct Arcades

Abstract

Ancient Roman engineers are famous for their use of arcades, or arched bridges, to elevate roads and aqueducts across valleys. The Romans first designed and built arches using stone blocks and then later changed to special concrete construction. In this paper, we illustrate how early unmortared arches could have been built using geometric design principles. This simplified analysis is sufficient to demonstrate, via retrospective analysis, the need for reconstruction efforts for arches violating these design criteria. Well-preserved remnants at the Simian Bridge and Vallon des Arcs arcades, located in southern France near Arles, are excellent examples of Roman arch engineering and are used as case studies to understand geometric arch design in practice. These arcades are vital parts of a larger aqueduct system used to provide the water-powered industrial Barbegal Mill and city of Arles with water in the first century A.D. Analysis of currently standing arches implies that Roman engineers may have relied extensively upon geometrical rules of thumb for design of these structures. In particular, modern stability analysis demonstrates the effectiveness of geometrical rules of thumb in determining structural failure requiring reconstruction at the Simian Bridge. The reconstruction that exists at the Simian bridge shows a shift from stone blocks to concrete. This shift may have occurred as a result of the Roman engineers’ increased awareness of geometrical criteria for arch design.