Jan 10, 1863 – The London Metropolitan Railway line began operation.
Constructing this subway caused a huge chaos in the city, mostly because the cut-and-cover principle was used. This method involved excavating a wide trench of 10 meters deep, laying the rails, lining up the walls with bricks and covering it all with arch roofs. Then the dirt was placed back and the roads were restored. The subway-line followed largely the main streets and almost never passed a building. The line connected the two stations of Paddington and Farringdon via Baker Street and King's Cross. Since the subway initially was served by steam locomotives, there were many places required were the steam could be vented safely. After 1905 this line and the meanwhile constructed other subway-lines were gradually electrified. Over the years this line was expanded many times, only thing different with the construction of the expanded subway-lines is that they were built using a tunneling shield.
As the underground expanded, construction technique changed. A tunneling shield was used. This shield has originally been invented by Marc Isambard Brunel, and perfected later by James Henry Greathead. This round iron shield advanced hydraulic, hundreds of feet under the ground, supporting the soft soil above. In the shield, construction workers placed cast-iron segments end to end, eventually forming a stiff waterproof tube. This technique has many advantages in comparison with the cut-and-cover method. Not only is this technique much less expensive and way faster, but it also doesn't completely destroy the surface above