But when it first opened in 1868, passengers could travel just five stops between South Kensington and Westminster.
Opening five years after the first Tube services of the Metropolitan Railway, the line was built by the Metropolitan District Railway.
The tunnels were made by digging a long trench, laying track and covering it over again.
The two companies initially worked together, sharing the Met’s steam trains, with the aim of completing a circle of underground tunnels in central London.
But by 1870, the two railway operators split – forcing the government to step in 14 years later to complete what is today known as the Circle line (more of that next week).
Meanwhile, the District line was extended east to Embankment, Temple and Blackfriars, west to Hammersmith, Richmond and Hounslow and south to Putney and Wimbledon.
By 1902, District line services had been extended to Upminster, although only for a brief period, as electrification of the line to East Ham meant this station soon became the eastern terminus.
It took another thirty years for District line services to return to Upminster, around the time that the modern Underground network was born with the creation of the London Passenger Board.
In that same year (1933), the Uxbridge and South Harrow branches transferred to the Piccadilly line.
Services to Hounslow were completely withdrawn in 1964 – leaving the District line route looking the same as it does today.
In 2003, the line was partly privatised in a public-private partnership managed by the Metronet consortium.
By 2007, Metronet had gone unto administration and TfL took over responsibility for its services.
The first walk-through air-conditioned trains were introduced on the line in 2013.,
The 40 mile route continues to operate daily services between Upminster, Ealing Broadway, Richmond and Wimbledon, with more than 220 million journeys taking place on the line annually.
Wimbledon branch trains also operate to Edgware Road, and services to and from Kensington (Olympia) operate at weekends and during special events.
Make sure to check our website at the same time next week to find out about the history of the Circle line.
