Electric locomotives were first used on the London Underground when the first deep-level tube line, the City and South London Railway (C&SLR), was opened in 1890. The first underground railways in London, the Metropolitan Railway (MR) and the District Railway (DR), used specially built steam locomotives to haul their trains through shallow tunnels which had many ventilation openings to allow steam and smoke to clear from the tunnels. It was impractical to use steam locomotives in the small unvented tubular tunnels of the deep-level lines, and the only options were rope haulage (as on the Glasgow Underground) or electric locomotives.