• When did the Circle line stop operating a continuous circular service?

The Circle line stopped operating a continuous circular service on 12 December 2009. The following day a new timetable was introduced. An extension opened to Hammersmith, and Circle line trains terminated at Edgware Road. 

The original circular service began in 1884 as the 'Inner Circle'. The name Circle line was first used on a poster in 1936. But it wasn't until 1949 that the line was formally included on the Underground map with a separate identity and yellow line colour. Although no longer a circular service, the name Circle line has been retained on the Tube map.