If you have ever visited Leonardo da Vinci’s Mona Lisa (1503) at the Louvre in Paris, you may have noticed a little mailbox in the room adjacent to the one that houses the famous painting. Believe it or not, this box isn’t used to collect feedback from visitors about their experience at the museum. It’s actually used to deposit fan mail.

The letters, which the museum stores inside its labyrinthine archive, come in many different shapes and sizes. Some leave unanswerable questions about Leonardo’s work, while others ask the polymath for life advice. Others still address their writing to the enigmatic woman in the painting, declaring their love and even asking for her hand in marriage. They write poems, sometimes accompanied by flowers or small mementos.

Leonardo’s portrait of Lisa Gherardini, the wife of a wealthy silk merchant from Florence, has captured people’s hearts for centuries. “This so soft a look,” the French writer Alfred Dumesnil noted in 1854, “but avid like the sea, devours.” Legend has it that, two years prior, the painting drove French artist Luc Maspero to jump out of his hotel window. “For years I have grappled desperately with her smile,” he allegedly wrote.

Part of Gherardini’s charm may be attributed to Leonardo’s mastery of sfumato, a painting technique meaning “vanished” or “evaporated”, where the artist creates imperceptibly small transitions between light and color to give their work an exceptional lifelike quality. In case of the Mona Lisa, the technique allowed Leonardo to capture the complexity of his subject’s expression.

Although nobody really knows when the mailbox was first installed, people have been leaving offerings to the painting since the 19^th century. Nowadays, you don’t need to travel to Paris to deposit your mail, you can send your love letter to the museum’s postal address, instead:

Musée du Louvre,

Service des publics,

A l’attention de Mona Lisa,

75058 Paris Cedex 01,

France