The City and South London Railway (C&SLR) was the first deep-level underground "tube" railway in the world, and the first major railway in the world to use electric traction. Originally intended for cable-hauled trains, the collapse of the cable contractor while the railway was under construction forced a change to electric traction before the line opened – an experimental technology at the time.
When opened in 1890, it served six stations and ran for a distance of 5.1 kilometres (3.2 mi) in a pair of tunnels between the City of London and Stockwell, passing under the River Thames. The diameter of the tunnels restricted the size of the trains and the small carriages with their high-backed seating were nicknamed padded cells. The railway was extended several times north and south; eventually serving 22 stations over a distance of 21.7 km (13.5 mi) from Camden Town in north London to Morden in Surrey.