Built as part of the Boston Elevated Railway, the Coolidge Corner Substation was one of six almost identical Georgian Revival–style buildings finished in 1911 that were designed to relay power from the South Boston Power Station to city trolley lines. The substation at 19 Webster Street remains the best preserved of the six, with only minor exterior changes, and is still a source of power for the MBTA Green Line trolleys that run along Beacon Street. Stone and Webster, electrical engineers with a national reputation, were the contractors for this station.