Construction began on the Hoosac Tunnel in Western Massachusetts in 1851. When it was completed in 1874, it was the second longest railroad tunnel in the world (the Mont Cenis railroad tunnel in Switzerland opened in 1871, and was 8.5 miles long.) This photograph of a Hoosac Tunnel construction site was taken in 1870. Engineers and workers pioneered many new technologies such as the compressed air drill, and the first commercial use of nitroglycerin, a powerful and very unstable explosive. Over 195 men lost their lives building the tunnel. Workers began digging from both ends of the mountai and when the two tunnels at last met in 1874, they were almost perfectly aligned, off by less than 1/2 inch.