The Dollis Brook Viaduct, also known as the Dollis Road Viaduct, Dollis Viaduct or Mill Hill Viaduct, is a railway viaduct to the west of Finchley, North London, United Kingdom. It carries the London Underground's Northern line from Mill Hill East station to Finchley Central station. It is the highest point on the London Underground above ground level, reaching nearly . It is located on a branch that was formerly part of the Edgware, Highgate and London Railway. Etymology The official name of the viaduct is taken from Dollis Brook which it crosses. The brook was marked on an 1877 Ordnance Survey map and the name may have originated from a farm called Dollis, previously in Hendon. This was earlier named Dalys in 1563, (the) Doles 1574, Dallys 1584 and in its current form of Dollis in 1822. This probably meant "the portions or shares of land (in the common field)", from the Middle English word dole. The name is not thought to be connected with the area of Dollis Hill, further south. Dollis Hill is thought to mean a "hill associated with a family called Dalley". History The viaduct was designed by John Fowler and Walter Brydone, chief engineer for the Great Northern Railway (GNR) from 1855 to 1861. The contractor that built the bridge was Smith, Knight & Co. The viaduct came into use on 22 August 1867 with the opening of the GNR's single-track Edgware, Highgate and London Railway line from Finsbury Park to Edgware, via Finchley and Mill Hill, which was authorised by an Act of Parliament in 1862. Although built to carry two tracks, the viaduct initially carried only one. Following the construction of a branch northwards from Finchley to Barnet in 1872, the original Edgware route effectively became a branch of the newer line. In the 1920s, the London and North Eastern Railway (LNER, successor to the GNR) planned to electrify the line but work was not carried out until the 1930s when the Northern Heights plan led to the doubling and electrification of the lines. This was in preparation for a transfer of the lines to the London Underground for it to form part of the system's Northern line. The start of the Second World War prevented the plans being completed and only the section of the line to Mill Hill East was electrified and reopened in 1941, whilst the High Barnet branch