Today, London Underground is a major business with three million passenger journeys made every day, serving 275 stations and over 408 km of railway.
Past and future
London has changed a lot since the first stretch of line - the Metropolitan, or Met - opened on 9 January 1863. The first stretch measured six kilometres (nearly four miles) and ran between Paddington (Bishop's Road) and Farringdon Street.
Cut and cover
To build the Met, streets along the route were dug up, tracks laid in a trench, covered with a brick-lined tunnel and the road surface replaced. Known as the 'cut and cover' method, this was quick and effective, but created as many problems as it was designed to solve. It caused congestion during construction and it was abandoned towards the end of the 19th century. By then, however, the Metropolitan was a success, stretching ever further across Middlesex, through Hertfordshire and into Buckinghamshire.
Other companies were keen to get involved and by Christmas 1868, the Metropolitan District had opened a line between Westminster and South Kensington.
This linked to a branch line from the original Met and some eastward extensions. These railways completed today's Circle line by 1884.
Once the system had started there was no stopping it and the search was on for further opportunities.
The Thames Tunnel
Twenty years before the Met steamed into history, Sir Marc Brunel - and his famous son Isambard - had built the Thames Tunnel between Rotherhithe and Wapping.
This was the first underwater tunnel in the world. The method used was similar to coal mining. Engineers sank vertical shafts and excavated the tunnels from within a metal shield. It is a tribute to the Brunels that major refurbishment to the tunnel was only needed during the 1990s.
Originally designed for horse-drawn traffic, it opened in 1843 for pedestrians, became a railway tunnel in 1869 and now carries the East London line.
The Brunel Engine House Museum, behind Rotherhithe tube station, tells the story of this unusual tunnel: one time banquet hall, shopping centre, and fairground.
In 1870 another sub-Thames railway opened. This had a cable-hauled line between the Tower of London and Bermondsey.
In marked contrast to the Thames Tunnel, this failed as an Underground line and was converted for pedestrian use after just a few months. It closed for good when Tower Bridge station opened in 1894.