For every few Picasso paintings that hang in a museum, there’s one that will never see the light of day. You can thank the world’s stealthiest art thieves for that. The Art Loss Register, the world’s largest database of stolen art, estimates that there are 350,000 pillaged works of art that have yet to be recovered. “We've seen art being traded for drugs, weapons, involved in the international terrorism trade, [and] traded for antiquities,” Chris Marinello, general counsel for the Art Loss Register, told ABC News in 2012.

While some of the most infamous art heists have taken place at museums around the world—including the theft of the Mona Lisa by a Louvre employee in 1911 and the 1990 heist at Boston’s Isabella Stewart Gardner Museum, in which more than $300 million worth of work was stolen—other pieces never even make it to a public viewing. Check out these Incredible Pieces of Art That Disappeared Before Making it Into a Museum because you'll probably never see them hanging on a wall.

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