A Kent Castle’s six-month programme of conservation work has helped historians unearth further artwork and etchings of French prisoners of war in the mid-18th century.

Sissinghurst Castle closed its doors to the public over the winter and discovered 18 graffiti pieces carved into the walls during the Seven Years War between 1756 and 1763.

Sixteen pieces of prisoner-of-war art had previously been discovered at the castle in Cranbrook and now all 34 graffiti images are being studied in detail.

The Seven Years War was the first worldwide conflict engulfing all of Europe and saw Britain and France fighting for each other’s colonial possessions abroad.

At the time, the castle, really just a stately home known as Sissinghurst Manor, was owned by Sir Horace Mann, but he never lived there, preferring to stay in Florence. So he leased the building to the Government, who converted it to a prison.

The camps were often manned by militiamen rather than regular soldiers and they grew a reputation for being much less disciplined and corrupt.

Kate Shaw, programming and marketing manager, said: “We closed for six months and we took part of the roof off the turret and plaster off the walls.

“We found a lot more graffiti on the walls than we thought we originally had. It was intact.

“It was a brutal time to be around. There were a few already at the castle and the archaeologists came in and found it had been engraved in the walls.

“It is a part of history and it is quite fundamental but it isn’t taught at schools.”

Up to 3,000 French PoWs are believed to have passed their captivity there, with officers housed in the tower, and other ranks in far more squalid conditions in the rest of the buildings.

Visitors to the National Trust property can still view their graffiti scratched into the tower’s walls, including a ship in full sail and several names and dates.

The men, writing home to their families, often referred to Sissinghurst as the Chateau de Sissinghurst. The name stuck and it is said to be thanks to them that it is now called Sissinghurst Castle.

An unknown number of them died during their imprisonment, and although they were buried in the grounds, the exact location of their graves is unknown.