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Not long after the Colonia Copia Felix Munatia Lugdunum, in present day Lyon, France, was founded in 43 BCE by Lucius Munantius Plancus on the 300 m high Fourvière hill overlooking the Saone and Rhône rivers and the plains to the north and east, it became the capital of the Gallia provinces, growing to be with some 50,000 inhabitants the largest town in Gaul. In the early days, the colonia on the west valleys surrounded Fourvière hill and depended on local springs, wells, and rain cisterns for its water provision, which soon became insufficient for the growing city. A first aqueduct was constructed in 20 BCE, bringing waters from a spring some 10 km north of the town. In the decades to follow, another three aqueducts were added. All of the aqueducts were equipped with one or more pressure lines and installations of (inverted) siphons, totaling nine, to cross valleys that were thought too deep or too wide for a bridge. Today, the Métropole de Lyon counts over a million inhabitants; it is after Paris and Marseille the third largest town in France. Since 1998, Lyon has been listed on the UNESCO World Heritage List, among others, because of the historic architecture in its urban settlements over 2000 years of age. This manuscript recounts the history and present remains of the four aqueducts and their nine extraordinary siphons, and is dedicated to Dr. Jean Burdy, who, with his team over many years of research of earlier literature and of investigations and discoveries of the physical remains of valley sites, produced a great number of publications saving the Lyon aqueducts from oblivion and leading to restorations in recent times. [ABSTRACT FROM AUTHOR]

In Roman times long distance water transport was realized by means of aqueducts. Water was conveyed in mortared open channels with a downward slope from spring to destination. Also wooden channels and clay pipelines were applied. The Aqua Appia, the oldest aqueduct of Rome, was constructed in the third Century BCE. During the Pax Romana (second Century CE), a time of little political turmoil, prosperity greatly increased, almost every town acquiring one or more aqueducts to meet the rising demand from the growth of population, the increasing number of public and private bath buildings, and the higher luxury level in general. Until today over 1600 aqueducts have been described, Gallia (France) alone counting more than 300. Whenever a valley was judged to be too wide or too deep to be crossed by a bridge, pressure lines known as 'inverted siphons' or simply 'siphons' were employed. These closed conduits transported water across a valley according the principle of communicating vessels. About 80 classical siphons are presently known with one out of twenty aqueducts being equipped with a siphon. After an introductory note about aqueducts in general, this report treats the ancient pressure conduit systems with the technical problems encountered in design and function, the techniques that the ancient engineers applied to cope with these problems, and the texts of the Roman author Vitruvius on the subject. Reviewers noted that the report is rather long, and it is. Yet to understand the difficulties that the engineers of those days encountered in view of the materials available for their siphons (stone, ceramics, lead), many a hydraulic aspect will be discussed. Aspects that for the modern hydraulic engineer may be common knowledge and of minor importance when constructing pressure lines, in view of modern construction materials. It was different in Vitruvius's days. [ABSTRACT FROM AUTHOR]