A 16th Century gatehouse is being saved from decay by a "thermal blanket" of plants.
Willimoteswick Gatehouse, near Haydon Bridge, Northumberland, was the birthplace of martyred Bishop Nicholas Ridley who was burnt at the stake.
In recent years the Grade 1 listed building has been crumbling and is being restored using an ancient technique.
Experts are soft-capping its brickwork with an insulating layer of plants.
The work is being carried out by Natural England and English Heritage.
Acting as a "blanket", soft capping uses plants such as sedum and stonecrop with shallow dense roots that naturally colonise on the tops of exposed walls.
The layer shields stonework from extremes of temperature and heavy rainfall, and helps insulate masonry, experts said.
Tom Gledhill, Natural England's historic environment specialist, said: "By retaining soft capping in the restoration work, we were able to protect both the historic and natural features of the site.
"Research clearly indicates that this technique is extremely beneficial to the long term conservation of ruined monuments, as well as making considerable savings in future maintenance and repair costs."
Bishop Ridley was burnt at the stake in Oxford in 1555 for refusing to renounce his protestant faith during Queen Mary's reign.