Every year, some 9 million visitors to the Louvre make their way into a gallery in which one small portrait—the lone painting on an immense freestanding wall—sits inside a bulletproof glass case, and is further protected by the watchful eyes of 24-hour security guards.
It is the most famous painting on earth and while it is unsigned, undated and unnamed, it is accepted as a masterful work by Leonardo da Vinci and known throughout the world as the Mona Lisa.