Gier: Durèze + Bozançon

The Gier was the youngest, longest and highest of the four aqueducts of Lugdunum and had been built in Opus Reticulatum in its whole line. In order to cross the many valleys in its 86 km course, four siphons and 25 bridges ware built. An overview:

Valley / River	Constructions	Siphon
Durèze	Detour plus siphon	Header tank plus venter bridge
Bozançon	Few bridges, also over side branches	-
Mornantet	Bridge	-
Garon	Siphon	Header tank 'La Gerle' plus venter bridge
Yzeron	Plat de l'Air-arcade, siphon	Header tank plus venter bridge Beaunant
Trion	Siphon	abutment of a header tank Fort Saint-Irénée

Over 50% of the aqueduct was subterranean, with 9 (perhaps 11) tunnels of different length. The deepest was built under the village Mornant just after the river-crossing with the Mornantet. During the construction of the tunnel of Saint-Martin-la-Plaine a miscalculation was made as can be seen on the photographs below.

Because of the total length of the aqueduct, the distance between and the diversity of the manholes could be studied in detail. Out of more than the estimated 1000 manholes, some 85 are known. Where the distance between two adjacent manholes could be measured, the result was between 76 and 78 m, whereas Vitruvius and Plinius indicated 240 Roman feet or 71 m. Jean Claude Litaudon hypothesizes that there were two kinds of manholes in the Gier aqueduct which alternated: the broader ones (3 Roman feet, 92 * 92 cm) with lowered bottom and the smaller ones (2,5 * 2,5 Roman feet, 77 * 77 cm) without. The first ones - a little bit broader than the aqueduct channel - served also as cleaning basins)*.

The Gier was the only aqueduct which also could serve the upper parts of Lugdunum on the Fourvière hill. Although its starting point was on 400 m above sea level, because of its constant and modest gradient the Gier delivered its water on 300 m above sea level, thus 20 - 40 m higher than the other three aqueducts.

Lyon-Gier aqueduct - LUGDUNUM

Génilac, Header tank	Génical, Header tank	Génilac, Header tank	Génilac, Header tank
Chagnon, Pierre de Chagnon	Chagnon, Pierre de Chagnon	Pierre de Chagnon	Chagnon, Cave de Curé
Chagnon, Cave de Curé	Chagnon, Cave de Curé	Durèze valley, venter bridge	Durèze valley, venter bridge
Saint-Martin-la-Plaine, Fontane tunnel	Saint-Martin-la-Plaine, Fontane tunnel	Saint-Joseph-le-Rieu, manhole	Saint-Joseph-le-Rieu, carved stone
Saint-Didier-sous-Riverie, bridge	Bridge over the Petit Bozançon	Saint-Didier-sous-Riverie, bridge	Saint Joseph / Saint-Didier
Saint Joseph / Saint-Didier	Saint-Maurice-sur-Dargoire, manhole	Saint-Maurice-sur-Dargoire, manhole	Saint-Maurice-sur-Dargoire, tunnel
Saint-Maurice-sur-Dargoire, bridge	Saint-Maurice-sur-Dargoire, bridge	Saint-Maurice, the 'Pont des Granges' I	Saint-Maurice, the 'Pont des Granges' II
Saint-Maurice, the 'Pont des Granges'	Saint-Maurice, the 'Pont des Granges'	Saint-Maurice, the 'Pont des Granges'	Mornant, Pont de la Condamine
Mornant, Pont de la Condamine	Mornant, Pont de la Condamine