The Hoosac Tunnel in Western Massachusetts was one of the great engineering marvels of the mid-19th century. It was first proposed in 1826, as a canal tunnel, but the Massachusetts State Legislature balked at the high cost. Construction finally began in 1851, as railroad interests demanded a northern route across the state. However, technical problems meant that significant progress was made only after 1866, with the introduction of nitroglycerine, used for blasting through rock. When the two ends of the tunnel were finally connected on November 27, 1873, they were only nine-sixteenths of an inch off, but it delayed completion for another two years. The tunnel It is four and three-quarters miles long, 22 feet wide at the base, and 24 feet high, and is still in use.