Tube staff are celebrating the 100th anniversary of London Underground's (LU) Piccadilly Line.
LU managing director Tim O'Toole was be at Leicester Square station and presented staff with a birthday card and a specially-designed cake.
The line opened on 15 December 1906 and consisted of less than 10 miles of twin tunnels running from Finsbury Park to Hammersmith.
The line is 45 miles long and has 52 stations.
A branch to Aldwych opened in 1907, but it was not until the 1930s that the line's rapid expansion began.
Art Deco stations
Extensions to South Harrow and Arnos Grove were opened in 1932 and to Hounslow West, Uxbridge and Cockfosters in 1933.
The 1930s also saw the construction of the Art Deco stations designed by Charles Holden, such as Arnos Grove, Southgate and Sudbury Town.
In more recent years, the line was extended from Hounslow West to Heathrow Airport (Terminals 1, 2 and 3 in 1977 and Terminal 4 in 1986). The new Terminal 5 station will open in May 2008.
About 540,000 passengers use the line every day.