The Circle line

The Circle line today is not so much a circle as a loose spiral, but its existence is fundamental to the history of the Underground. London’s two pioneering sub-surface lines – the Metropolitan and the District – each owned roughly half of it in the 19th century, and still share the stations and track. But since 1948 a third line has joined the District and the Met on the Tube map – the Circle.   

The loop was referred to as the Inner Circle in Parliamentary papers as early as 1864, but the Circle line name was not used officially until 1936. It was circular, or more accurately, elliptical, until 2009. 

When the mainline railways reached London in the 19th century their terminus stations were barred from the central area. The first two steam underground railways, the Metropolitan and the District, opened in the 1860s. Their shared ambition was to link the mainline railway companies’ terminus stations together in a circle.  

However, the two companies fell out over money, making this less of a priority for both. This meant the circle planned in 1864 was only completed after government intervention in 1884. When circular services first started, clockwise trains were run by the District Railway and anticlockwise by the Metropolitan Railway. There was fierce competition between them.  

Known informally as the Circle or Inner Circle since the 1880s, the shared loop was not formally named the Circle line until 1936. It was shown on the Tube map in the same green colour as the other sub-surface lines, the District, Metropolitan and Hammersmith & City lines. It became a separate distinct line in 1948, with the addition of a black border, finally turning the yellow we know today in 1949. Circle line trains were hand-me-downs from the other lines until a fleet of new C69 stock trains were delivered in 1970

On the morning of 7 July 2005, 15 people died in terrorist bomb attacks on two Circle line trains, at Edgware Road and near Aldgate. Bombs were also detonated on the Piccadilly line at Russell Square and on a bus nearby. In total, 56 people lost their lives.  

In December 2009 the closed loop of the line was changed to a loose spiral from Edgware Road to Hammersmith along part of the Hammersmith & City line. In 2013 new S stock trains started replacing the C stock, as part of Transport for London’s ambitious Four Line Modernisation (4LM) programme.