Long before it migrated to Edinburgh, the A720 was a link road in Lanarkshire. Starting on the A702 at Maidencoates between Abington and Roberton, a mile north of the A74 at Abington, the route headed north, staying on the west bank of the River Clyde, while the A702 crossed Clyde's Bridge to the east bank. It then passed through the small village of Roberton, and continued to wind northwards, crossing the B7055 (itself numbered shortly before the A720 ceased to be). No other places of any note were passed before the route ended at a fork on the A72 to the west of Symington where most traffic continued ahead for Lanark.
Both the A720 and the Symington to Lanark section of the A72 became part of an extended A73 in 1934.
The 1922 MOT Road List defines this route as: Junction with A72 near St John's Kirk - Roberton - Junction with A702 North of Abington An official document from 16/5/1934 details the following changes: The whole of this route to be renumbered as A73.