The 12 men formed a sophisticated network, and traveled to Britain from their Romanian base to commit the "high value and well-planned burglaries", according to London's Metropolitan Police.

Romanian prosecutors said last month they had recovered around 200, centuries-old first-edition books, a text by Italian scholar Petrarch, rare versions of Dante and 80 sketches by Spanish painter Francisco de Goya after they were stolen from a depot near London, in 2017.

The thieves often entered properties via the roof using ropes and ladders and also targeted smartphones, laptops and tablet computers, police added.

During the rare books raid, the thieves descended 12 meters to the ground after entering via the roof, dodging movement sensors to spend hours rummaging through thousands of works destined for an auction in the United States.

They left by the same route with a haul whose total value was estimated at around two million euros ($2.4 million).

The Metropolitan Police said the "irreplaceable" works had been "buried underground", posting a picture on its website of a hidden compartment under a house.

The court heard that the gang carried out their 12 raids in Britain between December 2016 and April 2019 at various locations including Peterborough, Hertfordshire and Enfield near London, and Sheffield, in northern England.

The gang flew members into Britain to carry out the robberies, jetting them out straight away afterwards.

"These sentences bring a successful conclusion to a complicated three-year investigation, which identified and convicted a previously unknown Romanian organized crime gang," said Detective Inspector Andy Durham, who led the investigation.

The men were sentenced over two days at Kingston Crown Court in southwest London having all been charged with one count of conspiracy to commit burglary and one count of conspiracy to conceal covert, disguise, transfer and remove criminal property.

They each received sentences ranging from three years and three months to five years and eight months.