The Mersey Railway was the first part of the passenger railway connecting the communities of Liverpool, Birkenhead, and now the rest of the Wirral Peninsula in England, which lie on opposite banks of the River Mersey, via the Mersey Railway Tunnel. The railway opened in 1886 with four stations using steam locomotives hauling unheated wooden carriages; in the next six years the line was extended and three more stations opened. Using the first tunnel under the Mersey the line is the world's oldest underground railway outside London.