The structure the canons built to capture water from the springs at the foot of Mont Sainte-Geneviève is remarkable and complex, extending more than 15 meters into the hillside. There can be no question of its identity since a military plan of c.1900 locates eight springhouses in the area and identifies the abbey’s as the ‘Source Saint-Jean’.

Deep in the hillside, water from at least five separate springs flows into two narrow, channelled corridors that open into a barrel-vaulted room serving as a collector. Water then flows through another, short, vaulted corridor into an enormous five-vesselled settling chamber. The central vessel is approximately 5 meters long by 3 meters wide. Water exited the settling chamber to flow in underground pipes down the slope of Mont Sainte-Genéviève to the Crise river, crossing it on a small now-destroyed bridge. From there, the water continued under pressure up the “Colline Saint-Jean” to the abbey.