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a tunnel constructed at the point where a navigation canal cuts through an upland or mountain range. The first canal tunnel, built in France in 1681, was approximately 160 m long and 6.7 m wide. The largest modern canal tunnel is the Rove Tunnel, constructed in the 1920’s on the Marseille-Aries Canal in France, which allows navigation by ships with displacements up to 1,000 tons; the tunnel is more than 7 km long and 22 m wide, with a height of 15.4 m (for a water depth of 4 m). Because of high construction costs and the necessity of ensuring safe operations, canal tunnels are usually designed for one-way traffic. Canal tunnels differ from conventional transportation tunnels in the shape of their cross section and in the reinforced waterproofing of the lower (underwater) part. Ships are usually moved through canal tunnels by special mechanical traction.