the london underground is a system of electric trains which are in london. it is the oldest underground railway in the world. it started running in 1863 as the "metropolitan railway". later, the system was copied in other cities, for example paris, new york, moscow and madrid. even though it is called the london underground about half of it is above the ground. the "tube" is the name used for the london underground, because the tunnels for some of the lines are round tubes running through the ground. the underground has got 274 stations and over 408 km of track. over one billion passengers used the underground each year.