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The Simplon Tunnel is an Alpine railway tunnel that connects the Swiss town of Brig with Domodossola in Italy, though its relatively straight trajectory does not run under Simplon Pass itself. It actually consists of two single-track tunnels built nearly 20 years apart. It was the longest railway tunnel in the world until the opening of the Daishimizu Tunnel in 1982.
A series of articles written about the Simplon Tunnel in The Engineer.
And a later article at The Engineer 1901/09/27.
A series called The Simplon Tunnel and Its Construction;