From its opening in 1845 to its demolition in 1897, the most prominent building on the square was the Boston and Maine Railroad depot. In 1893, the depot was replaced by North Union Station, several blocks to the north on Causeway Street. The depot was demolished to make way for construction of the Canal Street incline, the northern end of the Tremont Street subway, the predecessor to the MBTA Green Line. The Haymarket station on the subway line opened in 1898, with an entrance kiosk in the center of Haymarket Square. In 1902, the Haymarket Relief Station, a branch of Boston City Hospital, opened in a new building on the former site of the depot on the north side of the square.