The Piccadilly line on the London Underground opened on this day in 1906, serving 22 stations between Finsbury Park and Hammersmith. At first it was known as the Great Northern, Piccadilly & Brompton Railway.
The line was extended north-east to Cockfosters and west to Uxbridge and Hounslow West in the 1930s, a time when a forward-looking government decided to spend its way out of a dramatic recession. The extension west to Heathrow Airport was not added until 1977, with Terminal 5 added in 2008.
The line is one of the deepest in London, although of its 53 modern-day stations, only 25 are below ground.