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Heritage classified

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Origin and history

The Gier's aqueduct, built under the Emperors Trajan (from 110 AD) and possibly completed under Hadrian, is the longest (86 km) of the four aqueducts feeding Lugdunum (Ancient Lyon). It captures the waters of the Gier, tributing the Rhône, and crosses the Loire and Rhône departments with an average slope of 1.1 m/km. Its layout, reconstructed thanks to the remains and the eyes of the visit, reveals a variety of techniques: bridges-aqueducts, siphons (such as the Durèze or the Yzeron), tunnels and trenches. Recent excavations, such as the wood formwork dendrochronology (2018), confirm its Trajanian dating, although debates persist on a Augustian origin.

The most notable remains include the Beaunant Siphon Bridge (classified in 1875), the Arches of the Air Plat at Chaponost (classified in 1900), and the Soucieu Reservoir (1930). The lake passes through valleys which are covered by spectacular works, such as the Jurieux Canal Bridge or the Garon Siphon, whose arches are partially preserved. Protection points, such as the Pierre de Chagnon (1887) or the Pierre du Rieu (1996), attest to strict regulations for the preservation of the work, the resumption of a Augustian law prohibiting ploughing or construction nearby.

The study of the aqueduct began in the 16th century with Lyon scholars such as Pierre Sala (1520) or Guillaume du Choul (1538-1547), but it was Germain de Montauzan (thesis of 1908) who drew up an exhaustive map of it. Recent restorations, such as those of the Chaponost Arches (2001-2010) or the development of the Genilac section (classified in 1962), highlight its heritage importance. The aqueduct, symbol of Roman engineering, remains a subject of study for its redundant route (like the loop of Chagnon) and its mixed techniques (siphons, tunnels, bridges).

The monument is protected by several rankings under the Historical Monuments (1875 to 1986), and has been granted the Heritage Lotto for its preservation since 2018. Archaeological excavations, such as that of Beaunant's bridge-siphon (2018), reveal constructive details, such as wooden formwork or the reticulatum (paraly reticulated only in France). Today, sections such as the arches of the Air Plat or the Gerle reservoir are accessible to hikers, while others, such as the Saint Joseph section, remain fragile and partially buried.

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