The A1 is the most recent in a series of routes north out of London to York and beyond. It was designated in 1921 by the Ministry of Transport under the Great Britain road numbering scheme, comprising existing roads and streets, mostly historic, and later using stretches of purpose-built new roads in what is now the outer London borough of Barnet. The Archway Road section was built by Thomas Telford using Roman cement and gravel, an innovative technique that was used there for the first time, and is the basis for modern road building. The route closely follows the historic route of the Great North Road, though from 1954 it has diverted round the congested suburbs of Finchley and High Barnet along modern roads constructed in the 1920s and 1930s.