Union Square became a major commercial center during the early 19th century due to its location at an important crossroads. When the Warren Bridge opened to link Charlestown and Boston in 1828, it caused a considerable increase in traffic along Washington Street and Charlestown Lane (now Somerville Avenue). Railroad access began with the opening of the Fitchburg Railroad in 1843 and then opening of the Union Square railroad station just west of Webster Street. The Boynton Yards area south of the rail line and east of Union Square was created in 1874 when the swampy ground was filled with material from the top of Prospect Hill. It became a meat packing and manufacturing district, with a slaughterhouse, brickyard, glass shop, and later other industries.