Pierre Paul Riquet lives in Revel next to the watershed.
Between 1648 et 1660, he journeys through and over the Montagne Noire seeking water to supply the canal's navigation.

    Assisted in his research by the fontain designer, Pierre Campmas, they check on the water flow of the Fontaine La Grave, located 48.70 metres above the Garonne river near Monferrand, at Naurouze Sill.

    From the miniature dam they had built one day, a stone fell. To his satisfaction Pierre Paul Riquet sees that the water flows on both sides : to the Méditerranean and to the Atlantic océan.