Circle line (London Underground)

The Circle line is a London Underground line, running in a roughly circular route around central London. It was first opened in 1884 as the Metropolitan District Railway, and initially consisted of separate lines operated by the Metropolitan Railway and the District Railway. The line fully separated and was named the Circle line in 1949.

The line is coloured yellow on the London Underground map. It shares much of its track with the District, Hammersmith & City, and Metropolitan lines, creating a complex operational environment. Trains typically operate in both clockwise and anticlockwise directions.

Historically, the Circle line operated a simple continuous loop, but in December 2009, the line was extended to include a section of the Hammersmith & City line, creating a "spiral" route terminating at Hammersmith via Aldgate. This change aimed to improve reliability and increase capacity.

The Circle line serves many of London's major railway stations, including Paddington, Euston, King's Cross St. Pancras, Liverpool Street, and Victoria. It also provides access to numerous tourist attractions and important business districts. Because it directly connects numerous mainline terminals, it's a key service for onward travel across the UK.

The line is operated by Transport for London (TfL). Rolling stock on the Circle line consists of S7 Stock trains, which are air-conditioned and equipped with walk-through carriages.