Siphons

The Romans used siphons throughout the empire, and were especially numerous in Gaul, but relatively rare in Rome (Hodge, 2002). The siphons included a header tank for transitioning the open channel flow of the aqueduct into one or more pipes, the bends called geniculus, the venter bridge to support the pipes in the valley, and the transition of pipe flow to open channel flow using a receiving tank.

One of the largest siphons was the Beaunant siphon of the aqueduct of the Gier River which supplied the Roman city of Lugdunum (Lyon, France). Figure 7.5 shows the siphon ramp (with nine lead pipes), the header tank, and the venter bridge. This siphon was 2,600 m long and 123 m deep with an estimated (Hodge, 2002) discharge of 25,000 m3/24 hour. Total length of the nine parallel pipes was 2.6 km. The largest siphon was built at Pergamon (Madradag) which was 3,000 m long and 190 m deep and only had one pipe compared to the 9 pipes at Beaunant.

Fig. 7.5 Siphon of aqueduct of Gier, Beaunant, France near Lyon (Ancient Lugdunum). (a) This reconstruction shows ramp of siphon with header tank on the top and the nine lead pipes of the siphon (Haberey, 1972 based upon Montauzean, 1908). (b) Ramp of the siphon near Chaponost. (Copyright permission with L. W. Mays) (c) The venter bridge of the siphon near Beaumont. (Photo courtesy of with H. Fahlbusch)