Essential works will get under way next week to Dry Arch Bridge, a single span, 18th Century link on the A363.
The work will include repairs to the stone masonry, drainage improvements and the installation of highway kerbs to each side of the carriageway.
Two-way signals will be installed while the work is carried out. It will start on September 4 and is expected to last until November 24, 2017.
Drivers have been advised to expect delays but the Council is working with the contractor to minimise disruption.
The bridge also carries a public bridleway which will remain open throughout the works.