This boat lift (1887) on the Canal de Neuffossé replaced the five locks that, until 1967, were necessary for barges to pass a 13m difference in levels. The principle was simple: the barges moved into two lock chambers or pools filled with water, which were fixed onto two enormous pistons that created a set of hydraulic scales of sorts. One of the lock chambers would rise as the other went down. Nowadays, a giant lock 500m upstream can deal with six barges at a time.