In the year 1393, the heads of the families of the Central Valley District, which included the hill area of Saint-Vincent and Émarèse and of Challand-Saint-Anselme, asked Ibleto of Challant the permission to use the waters arriving from the the Ventina glacier, sited in the high Valley, to solve the serious problems of drought for their lands, through the construction of a canal (“rû”). The great work of construction started about forty years later, with the authorization act drafted by Francesco of Challant in 1433, and lasted forty more years. The canal unwinds over the territory of Ayas and Brusson for about 25 kilometers, starting from the Courtod Gorge, at a height of 2,100 meters, and canalizes the waters of the torrent that comes down from the Cime Bianche. Originally the watercourse, once arrived to the Col of Joux, would split up in three branches, the main of which would serve Saint-Vincent, while the other two, respectively, served Émarèse and Arbaz: these latter became inactive in the 17th century during the years of the plague (1629-1630). The construction and maintenance of the canal were done through the technique of the “corvées”, the days of work that, in the old days, farmers had to carry out in favor of the feudatory, and which instead were now rendered for a work of public utility. The canal used to be watched over by two guardians who, during the periods in which it was filled up with water, used to cover it all along its length. It is possible to cover most of the route of the “rû” starting from the Courtod Alp - 2,014 meters – a mountain pasture sited above Saint-Jacques, entering the trail to the Grand-Tournalin Refuge, following on then along the canal, in the direction of the valley floor (trail #5 – route duration: 2½ hours).