Canton Viaduct is a blind arcade cavity wall railroad viaduct in Canton, Massachusetts, built in 1834–35 for the Boston and Providence Railroad (B&P). At its completion, it was the longest (615 ft [187 m]) and tallest (70 ft [21 m]) railroad viaduct in the world; today, it is the last surviving viaduct of its kind. It has been in continuous service for 187 years; it now carries high-speed passenger and freight rail service. It supports a train deck about 60 feet (18 m) above the Canton River, the east branch (tributary) of the Neponset River. The stream pool passes through six semi-circular portals in the viaduct.