The United Kingdom has the world’s oldest continuously operating underground railway, the London Underground.
The first section opened on 10 January 1863 between Paddington and Farringdon. It was operated by the Metropolitan Railway, whose name later inspired the word “metro” in many languages. Early trains were powered by steam, requiring ventilation shafts and open sections to manage smoke.
Electrification arrived in the late 19th and early 20th centuries, allowing deeper tunnels and cleaner operation. The network expanded through mergers and new construction, eventually becoming the system commonly called the Tube. Its famous roundel symbol and colored line map are now internationally recognizable.
The London Underground is not entirely underground: substantial sections run above ground, especially in outer London. The system has 11 lines and serves hundreds of stations. London’s first underground railway predates subway systems in cities such as Paris, New York, and Berlin.