The City and South London Railway (carriage pictured), the first deep-level underground railway in the world, officially opened, running 3.2 mi (5.1 km) between the City of London and Stockwell.

The City and South London Railway (C&SLR) was the first successful deep-level underground "tube" railway in the world, and the first major railway to use electric traction. The railway was originally intended for cable-hauled trains, but owing to the bankruptcy of the cable contractor during construction, a system of electric traction using electric locomotives – an experimental technology at the time – was chosen instead.

Rapid transit or mass rapid transit (MRT) or heavy rail, commonly referred to as metro, is a type of high-capacity public transport that is generally built in urban areas. A grade separated rapid transit line below ground surface through a tunnel can be regionally called a subway, tube, metro or underground. They are sometimes grade-separated on elevated railways, in which case some are referred to as el trains – short for "elevated" – or skytrains. Rapid transit systems are usually electric railways that, unlike buses or trams, operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles.

The City of London, is a city, ceremonial county and local government district in England. Established by the Romans around 47 AD as Londinium, it forms the historic centre of the wider London metropolis. Surrounded by the modern ceremonial county of Greater London, from which it remains separate, the City is a unique local authority area governed by the City of London Corporation, which is led by the Lord Mayor of London; although it forms part of the region governed by the Greater London Authority.

Stockwell is a district located in South London, part of the London Borough of Lambeth, England. It is situated 2.4 miles (3.9 km) south of Charing Cross.