Hydraulic engineering of inverted siphons in Roman age: a review

In this work the authors wish to present a technology, less known if compared with the Roman age arcaded bridges used to cross broad and deep valleys: the inverted siphons. These structures are very complex hydraulic systems: for their good functioning, in fact, not only adequate constructing tricks were necessary, but also good theoretical knowledge, to be applied during the planning stage. In particular the systems that will be examined in this work are the double inverted siphon of the Yzeron aqueduct (Lyon, France) and the triple inverted siphon of Aspendos (Turkey); in both cases the Roman engineers ensured the correct functioning of the systems relying on specific technical solutions. Besides, the Barratina (Termini Imerese, Italy) siphon will be shortly presented, that is a “mixed” siphon whose technical conception distinguished it from the others. The Barratina siphon is the only case so far known in the history of the Roman aqueducts where the receiving tank is above the hydraulic grade line; nevertheless in many cases a precise leveling was not executed. It still possible that in the territory of the Roman Empire, other similar solutions can be found.