Ninebanks Tower and the Whitesyke and Bentyfield lead mines
Work has begun to protect four ancient monuments in the North Pennines which have suffered centuries of bad weather.
They are Whitesyke and Bentyfield lead mines in Cumbria, Shildon engine house and Ninebanks Tower in Northumberland and Muggleswick Grange, County Durham.
All are currently included on English Heritage's At Risk Register.
Specialist contractors have been brought in to clear the sites of vegetation and consolidate unstable sections of stonework.
Restoration work, funded by the Heritage Lottery Fund, has already been delayed by more than a month because of recent bad weather.
Jon Charlton, of the AONB Partnership, said: "These buildings taken together really tell the story of the North Pennines, how our ancestors down the ages lived and worked in the area.
"Over time they would have crumbled and disappeared completely.
"We want to protect what remains so that we and future generations can see these legacies in the landscape of what it was like to live those past lives."
Archaeologists will also be working at all four sites and are hoping to uncover some new insights into the ways the buildings were used.
Shildon Engine House and Muggleswick Grange
Muggleswick Grange, near Consett, was built during the mid-1200s for the Prior of Durham and originally lay in the grounds of an enclosed park. It is considered of national importance because standing remains of monastic granges from this time are very unusual.
The sandstone Ninebanks Tower is all that remains above ground of a large medieval house, to which the tower was added in about 1520.
Shildon Engine House, near Blanchland, was built around 1805 to house a Cornish pumping engine which kept the network of lead mines operating underneath from flooding.
The remains of the Whitesyke and Bentyfield mines, near Alston, once formed part of an extensive complex of more than 100 lead mines operating in the area during the 18th and 19th Centuries.