The Metropolitan Railway, the world's first underground railway, opened in London in 1863.
The first section ran between Paddington and Farringdon, a distance of about 3.75 miles. It was built mainly by the cut-and-cover method: workers dug a trench, constructed the railway, and covered it again. Steam locomotives hauled trains through the tunnels, so ventilation shafts and open sections were important.
The railway was created to relieve severe congestion caused by horse-drawn traffic in central London. Its success encouraged other companies to build underground routes, eventually producing the network now known as the London Underground. The Metropolitan Railway itself later became the Metropolitan line.
A common mix-up is to identify 1890 as the opening date of the Underground. That year belongs to the City and South London Railway, the first deep-level electric railway. The 1863 Metropolitan Railway was earlier and used shallow tunnels with steam traction.