On this day in 1911:The theft of Leonardo da Vinci’s “Mona Lisa” is discovered in what has been described as the greatest art heist of the 20th century.

A day earlier, Vincenzo Peruggia, a former Louvre worker, walked into the Paris museum and noticed an absence of guards or visitors. He took the painting off its pegs, removed it from the frame, and walked out of the Louvre with it under his arm.