Week in Insights: Now You See It, Now You Don’t

There are more than 35,000 works of art in the Musée du Louvre, but none is more recognizable than the “Mona Lisa.”

Visitors at the Louvre examining the The Mona Lisa, or “La Joconde,” by Italian artist Leonardo Da Vinci.

Photographer: Marc Piasecki via Getty Images

That hasn’t always been the case.

On Aug. 21, 1911, a thief removed the small painting—it’s just 30 inches by 21 inches—from the wall, wrapped it in his clothing, and walked out of the door. The museum was closed that day since it was a Monday. Workers at the Louvre wouldn’t notice its disappearance until the next day.

The thief, Vincenzo Peruggia, was a handyman who had worked for the Louvre. He had hidden in ...