An investigation is starting at a historic wall which has a "considerable lean" in places, a council said.
The work at the old Ludlow Town Wall in Shropshire will confirm its thickness before a strengthening scheme starts.
In February part of the Castle Square Car Park closest to the wall was fenced off to reduce the risk of traffic loading affecting the wall's stability.
Some work as part of the improvement scheme will take place in late spring 2011, Shropshire Council estimates.
The majority of the work in the proposed strengthening and refurbishment project would take place in the autumn and winter this year, the authority said.
The investigation work in connection with the scheduled ancient monument was starting on Monday and expected to last for about one to two weeks.
It will also enable engineers to understand the nature of the soil.