The Boston and Lowell Railroad (B&L) purchased the Mystic River Railroad, an unbuilt paper railroad, in 1871. It constructed the line from Milk Row station around Charlestown to a new freight terminal built on filled land in the Mystic River between the two channels. After a legal battle with the Lynn and Boston Railroad about the right to cross its tracks, the B&L extended the branch across the Mystic Bridge, allowing ships to dock without passing through any bridges. As the B&L and its successor Boston and Maine Railroad (B&M) expanded Mystic Wharf in the 1880s, replacing the middle section of the bridge with a roadway on filled land, the grade crossings became a significant inconvenience and hazard to bridge traffic.