A tunnel-canal is an underground structure designed to allow boats to pass under a mountain rather than around it. In Provence, between Marseille and the Étang de Berre, one such structure has been dormant for over sixty years under the chain of the Estaque. Known as the Rove tunnel, it holds a record that has never been surpassed: it is the longest tunnel-canal in the world, with a length of 7,120 meters. This engineering feat, built in the early twentieth century, was completed in 1926 after a construction period that was significantly delayed by World War I. Despite its impressive size and technical achievements, the tunnel was in use for only about forty years before a collapse in 1963 blocked it permanently. The Rove tunnel is a maritime tunnel-canal carved beneath the Estaque mountains, connecting the northern harbor of Marseille to the Étang de Berre, a large lagoon in the Bouches-du-Rhône region. Its southern entrance is located in the Riaux neighborhood of Marseille, near the Estaque, while its northern end opens at Marignane, near the Étang de Bolmon. The tunnel is completely straight, with no turns, and has dimensions of 22 meters wide, 15 meters high, and 4 meters deep. These dimensions allowed two 1,500-ton barges to pass each other inside the tunnel, a remarkable technical achievement for its time. The tunnel was built by Léon Chagnaud, a senator and entrepreneur, as part of the Marseille-Rhône canal project, which aimed to connect Marseille directly to the Rhône River without going through the sea. The construction of the Rove tunnel was a massive undertaking that involved thousands of workers, many of whom faced difficult and dangerous conditions. Strikes and accidents were common, and progress was significantly slowed by World War I, which diverted resources and labor to the war effort. Despite these challenges, the tunnel was completed in 1926 and put into service the following year. However, its operational life was relatively short, lasting less than forty years before a collapse in 1963 ended its use. The collapse occurred in a particularly unstable area of marly terrain, creating a crater 15 meters deep on the surface and blocking the tunnel entirely. Although the collapse marked the end of the tunnel's active history, it was not due to the cost of repairs. Instead, changes in regional economic needs made the tunnel unnecessary for river traffic. The expansion of the Rhône River and the growth of the port of Fos-sur-Mer reduced the need for the tunnel, and even if it had remained intact, it would likely have fallen into disuse. Now, after more than six decades of silence, the Rove tunnel may have a new purpose. A project led by Gipreb and the South Region aims to partially reopen the tunnel to allow seawater to flow through it, helping to restore the fragile ecosystem of the Étang de Berre. This transformation would give the tunnel a new function as an environmental regulator rather than a navigation route. While the Rove tunnel remains a silent witness to its unchallenged world record, its future may offer a new, ecological utility.