"Crumbling" graffiti drawn by conscientious objectors held in Richmond Castle during World War One is to be preserved by English Heritage.
In May 1916, 16 men - mainly from the north of England - were incarcerated in cells at the North Yorkshire castle.
The graffiti features pencil drawings and inscriptions, including slogans, poetry, and portraits of loved ones.
A grant of £365,400 from the Heritage Lottery Fund will be used to protect the work and allow public access.
The prisoners, known as the Richmond Sixteen, included a Sunderland footballer, a clerk at the Rowntree's chocolate factory in York, a bookseller from Ely and men of faith.
Kate Mavor, English Heritage's chief executive, said the graffiti was an "important record of the voices of dissent" during the war.
She said it was vital to preserve "these delicate drawings" to ensure the stories were not lost.
High levels of moisture and damp meant the layers of lime wash and plaster on the walls were crumbling and flaking off, she added.
Sunderland centre-forward Norman Gaudie, a Quaker, was one of the men held at Richmond Castle before being shipped to France to face court-martial and the threat of firing squad.
His daughter-in-law, Marjorie Gaudie, said: "It is important to remember men like Norman. They were courageous men.
"He acted from the deepest conviction that all life is sacred. He knew it was wrong to take a life and so he refused to fight."
"He was prepared to die for his belief and that took immense courage," she added.
The men were sent to France on 29 May 1916 and a few weeks later were sentenced to death by firing squad, which was immediately commuted to 10 years hard labour under orders from Prime Minister Herbert Asquith.
Most ended up at Dyce Camp, near Aberdeen, Scotland, where their punishment was to break rocks in a granite quarry and suffer the indignity of being branded as "degenerates" by the local press.