Circle line (London Underground) and the C Stock trains have recently been replaced by new seven-car S Stock trains, in a programme completed in 2015. In 1863 the Metropolitan Railway, the world's first underground railway, opened in London between Paddington and Farringdon, connecting the Great Western Railway's relatively remote terminus at Paddington with Euston and King's Cross stations and the City, London's financial heart. In the same year a select committee report recommended an 'inner circle' of railway lines connecting the London termini that had been built or under construction. In the next year the Metropolitan District Railway (commonly known as the District Railway)
Line C (Buenos Aires Underground) Line C (Buenos Aires Underground) Line C of the Buenos Aires Underground, that runs from Retiro to Constitución terminus, opened on 9 November 1934, and it has a length of . It runs under such streets as Lima Sur, Bernardo de Irigoyen, Carlos Pellegrini, Esmeralda, la Plaza San Martín and Avenida Ramos Mejia. It not only connects to every other line on the system (with the exception of Line H, which will be connected at a later date), but its termini at Retiro and Constitución also connect it to some of the most important commuter rail networks in Buenos Aires,