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Origin and history

The lake of the Yzeron, sometimes called the aqueduct of Craponne, is one of four ancient aqueducts serving Lugdunum (Lyon). Unlike others, it is distinguished by its branched structure, capturing water from the basin of the Yzeron and its tributaries. Its branches confluence at Grézieu-la-Varenne and Craponne, where remains of the tourillons, remains of a double siphon with intermediate reservoir. Its construction, dated between 21 B.C. and 30 A.C., makes it the second Lyon aqueduct chronologically built under Augustus.

The existence of this aqueduct has long been controversial. As early as 1520, Pierre Sala evokes the "roix tower" (tourillons) as remains of water pipes, but Guillaume Delorme (1760) and François Gabut (1880) consider them imaginary or linked to rural villas. Jérôme Chipier (1862) and Baron Raverat (1887) defended his route, before Germain de Montauzan confirmed his role in the feeding of Lugdunum in 1908. Recent studies (2023), combining carbon 14 and dendrochronology, confirm its construction around the change of the era.

With a length of 26 to 40 km depending on the branches, the water was leaving at an altitude of 710 to 715 metres, requiring break-slope falls to limit wear. Its estimated flow rate between 12,000 and 15,000 m3/day was in the present Lyon district of Point-du-Jour. The remains classified (1982) in Craponne, like the two piles of the tourillons, illustrate its system of successive siphons, unique among the Lyon aqueducts.

It crosses eight municipalities, including Yzeron, Vaugneray, and Francheville, before reaching Lyon. Its layout, studied by Montauzan, reveals an engineering adapted to an rugged terrain, with multiple captures (Pollyonnay, Vaugneray). Despite initial debates about its destination, its role in Lugdunum's urban supply is now admitted, complementing that of the Gier, Brévenne and Monts d'Or aqueducts.

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