“The Stonemason’s Yard” was one of many paintings that officials took from the National Gallery in London and moved underground to keep safe from Nazi forces

Canaletto’s 18th century painting, The Stonemason’s Yard, depicts stone workers in a Venetian city square.  The National Gallery, London

A Canaletto painting that spent four years hidden in a Welsh slate mine during World War II is returning to the country for a show at the National Library of Wales in Aberystwyth.

The painting, The Stonemason’s Yard (c. 1725) hung at the National Gallery in London in the early 20th century before British authorities transported it to Wales.

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Canaletto was a Venetian artist known for his austere cityscapes. In The Stonemason’s Yard, he depicts a scene of figures at work in the Campo San Vidal, a square of the city. The piece is a portal into everyday life in 18th century Venice.

In the lead up to World War II, the British government brainstormed ways to keep important museum treasures safe. One idea was to send the art to Canada, but that plan was turned down due to concerns over U-boat attacks during transportation. According to the National Gallery, Winston Churchill declared, “Hide them in caves and cellars, but not one picture shall leave this island.”

Officials landed on the Manod quarry, a mine in north Wales, as the best location. Experts used explosives to make the mine entrance larger and built brick rooms inside so that the paintings would be better protected from temperature shifts.

“They had to control the climate within the quarry to make sure that these paintings were fine,” Mari Elin Jones, National Library of Wales interpretation officer, tells the Guardian’s Steven Morris. “They learned a lot about humidity control and temperature control and how that affected works. It was more than just stick them in, stick them in a quarry and hope they’re all right.”

Paintings entered the mine in the summer of 1941 and didn’t come out until after the war ended in 1945. Following the war, The Stonemason’s Yard returned to London’s National Gallery.

Now, 80 years later, the National Gallery is loaning Canaletto’s piece to the National Library of Wales as part of its 200th anniversary festivities.

“Being able to welcome Canaletto’s masterpiece back to Wales after having taken refuge here 80 years ago is tremendously exciting, and we cannot wait to share with the public this fascinating story,” says Jones in a statement.

The painting will hang in the library’s Gregynog Gallery with modern pieces, as well as notable works from 18th and 19th century artists, including Richard Wilson, Penry Williams and J. M. W. Turner. The exhibition, on view from May 10 to September 7, displays Welsh landscapes from the library’s collection and shows comparisons and links to The Stonemason’s Yard.

“It is a beautiful portrait of a city, but it’s also a lovely portrait of the people that made that city, a celebration not only of the picturesque but of industry as well,” Jones tells the Guardian. 

She adds, “Industry has shaped the way our country looks and shaped modern Wales. We’d be nothing without our industry.”