Repair work is to begin on a partly-medieval bridge in Oundle next week.
The work to South Bridge will strengthen the damaged structure while maintaining the fabric of the scheduled ancient monument.
Northamptonshire County Council is carrying out preliminary work on May 19 after English Heritage approved outline plans for the sensitive renovation to take place.
The road over the bridge will be closed next week while the work takes place.
Deputy leader of the county council Cllr Heather Smith said: “We’ve been liaising very closely with Oundle Town Council, East Northamptonshire District Council and English Heritage, which have played roles in co-ordinating this work.
“Because of the specialist nature of the structure it has been a challenge to find an approach that allows a robust engineering solution while not detracting from its historical importance.”
Leader of East Northamptonshire Council Steven North said: “We’re delighted work is starting on this historical gateway into Oundle.
“The bridge is a vital link into the town and once fully restored will help residents and visitors access the town and all the facilities that Oundle has to offer.”
Preparations include undertaking trial holes to establish the nature of the materials of which the bridge is composed.
South Bridge was closed to traffic between March and December 2011 for urgent repairs following a water main fracture.
The bridge is a seven-arch masonry structure, parts of which are thought to date back to medieval times. It is a scheduled ancient monument and is also Grade II listed.
At the time of the fracture there was evidence to suggest sufficient damage had been caused to the make the bridge unsafe to traffic and an emergency road closure was put in place.
Following the repair of the water main a detailed inspection of the bridge was conducted.
This revealed several defects within the arch directly below the fracture, including carriageway settlement and arch cracking.
The inspection also showed that several arches exhibited cracking and other stone work defects.
A structural assessment was undertaken and this indicated the bridge had a very low load-carrying capacity.
Since December 2011 a three-tonne weight limit has been in place with bollards restricting the type of vehicle that can use the bridge.
Once the repairs are complete the bridge will have an 18 tonne weight limit at the request of Oundle Town Council. This will help prevent further damage to the structure.