The Baltimore Belt Line was constructed by the Baltimore and Ohio Railroad (B&O) in the early 1890s to connect the railroad's newly constructed line to Philadelphia and New York City/Jersey City with the rest of the railroad at Baltimore, Maryland. It included the Howard Street Tunnel, the Mount Royal Station for B&O's Royal Blue Line passenger trains, and the first mainline railroad electrification in the United States. The line is currently operated by CSX Transportation as part of its Baltimore Terminal Subdivision. Origins The B&O's original connection to New York in Baltimore was through surface street transfers to the old Philadelphia, Wilmington and Baltimore Railroad (PW&B), with passenger / freight cars (also known then as rail carriages) pulled by horses along the east–west running East Pratt Street route, first between the B&O's old Pratt Street Depot at Pratt and South Charles Streets, then later using the new terminal and B.& O.'s general headquarters of Camden Street Station (built 1857–1865) to the PW&B's President Street Station (built 1849–1850) at President and Fleet Streets, east of the harbor past the waterfront piers from the early 1830s to early 1870s. This transfer process was also used because of ordinances passed by the Baltimore City Council in 1831 prohibiting the use of early steam locomotives within the city limits on downtown streets in the more primitive years of early American railroading. In 1884, the PW&B was purchased and absorbed by the Pennsylvania Railroad (PRR), the growing dominant regional line in the Northeast states and a major rival of the B&O, and the PRR cut off the connection to the East Coast seaboard's main line. The B&O then proceeded to build its Philadelphia Branch (formally known as the Baltimore and Philadelphia Railroad) to connect to the Philadelphia and Reading Railroad, in turn connecting with the Central Railroad of New Jersey for B&O's New York service across the Hudson River to Manhattan. The combination also provided a connection to the Staten Island Railway, which served as the terminal switching company for the B&O's New York freight service across the Hudson River or Upper New York Bay to Manhattan. New B&O president Charles F. Mayer made the Belt Line a priority by the 1870s, and recruited young railroader Samuel Rea to work on it as Chief Engineer. Construction Connecting the new Philadelphia Branch to the rest of the B&O system was a considerable engineering challenge. A new