Leonardo da Vinci painted the Mona Lisa sometime between 1503 and 1509. Legend has it he liked the painting so much, that he kept it, taking it with him when he was invited to visit the court of François I, in 1516. Why did Da Vinci love this portrait? Numerous theories have come and gone over the years, but one thing that’s for certain is the Mona Lisa was a groundbreaking work in its time. Just a few decades before in Italy, the Renaissance had begun, bringing with it a love of the classical, balance, and proportions. Lovely as the works produced in its early decades were (think, for example, of Botticelli’s famous Birth of Venus), they still had a certain stiffness, an idealized beauty that kept them from being totally true to life.

With Lisa, Da Vinci used revolutionary experiments in shading and technique, to produce an atmospheric effect in which borders between objects are blurred and more real-looking, rather than outlined. This is typically referred to as sfumato, from the Italian for “smoky”. Something else helped the painting to be true-to-life: Though in Da Vinci’s time, the Church had ruled that human dissection was forbidden, the artist secretly studied cadavers. This taught him how to capture features such as the veins in his sitter’s hands, and even the texture of her skin. But for all these features that make the portrait look like a window into the world, there are also carefully planned angles and proportions, including measurements based on the golden mean and other important geometric ratios. The Mona Lisa was also unique in its time because of the landscape in the background – it corresponds to no real place on earth (some have even described it as “lunar”), and can be considered utterly an invention of Da Vinci’s, and not a real place. This is revolutionary when you consider that, in that era, portraits and narrative pictures (even of mythological or religious subjects) often featured actual local sites and cities in their backgrounds.

But of course, the most astounding thing about the portrait is Lisa’s smile…or lack thereof.

No one knows exactly what this mysterious woman’s expression implies. Is she holding back a grin brought on by the musicians and clowns Leonardo allegedly brought in to entertain her while she sat? Does her smile imply a joke – that she is really an imaginary portrait of Da Vinci himself as a woman? This idea is supported by Brown’s characters, since it would symbolize the union of the male and female. Or is she merely keeping her lips closed to conceal bad teeth? All of these are actual theories that have been suggested over time. And there are countless other ones out there.

If it’s not merely a portrait of Leonardo dressed in drag, who was the woman who sat for the Mona Lisa? Most people believe she is Madonna (“My lady”) Lisa Gherardini, wife of Florentine silk merchant Francesco del Giocondo. This is why the painting is known as “La Gioconda ” in Italian, and “La Jaconde” in French. However, the name may merely have come into being to describe what some would say is the woman’s attitude: “jocund” (merry).

The mysteries behind it add to its allure, but ultimately what matters is La Gioconda’s appeal. As a contemporary of Da Vinci’s once said, the painting looks so real, one wants to carefully regard Mona’s throat to see if she’s actually breathing.

Unfortunately, this kind of close inspection isn’t very easy today. From Da Vinci’s studio in Italy, to Fontainbleu and Versailles, to the palace that formerly stood in the Jardin des Tuileries, the Mona Lisa at last came to the Louvre in the 19th century, and today she is still there, protected by a huge, thick, slightly tinted bulletproof glass encasement…not to mention blocked by huge crowds of enthusiastic viewers from around the world. The glass case protects Mona’s pigments from fading due to constant exposure to camera flashes. It is carefully climate-controlled to keep the wood she’s painted on from warping due to heat and humidity. It also protects her from theft.

Yes, theft. The Mona Lisa was once stolen, right from the Louvre. This now little-known fact was one of the hottest stories of the day back when it happened in late 1911. One August morning, guards and visitors came into the Louvre to find the Mona Lisa missing, and only nails left hanging on the bare wall where she used to be. Her frame was later found in a back stairwell. But there was no sign of the masterpiece.

Theories abounded as to where the painting had disappeared to. Some said it was the work of anarchists, who ran rampant in early 20th century Paris. Many artists were anarchists in their own way; for example, Marinetti, an Italian Futurist, once said, “a roaring car that seems to ride on grapeshot is more beautiful than the Victory of Samothrace.” And so, many minds turned to the art world to find their suspect. Could the kidnapping of the Mona Lisa have been an extreme statement that old ideas about art needed to be overturned? If this was the case, who better to suspect than super-avant garde artist Pablo Picasso?

He and his friend, poet Guillaume Apollinaire, were fascinated by the Louvre’s collection of African and tribal art and artifacts. And lucky for them, the Louvre’s security at the turn of the century was negligent at best. Apollinaire’s secretary was often able to filch small sculptures for his employer! It’s said that Picasso once jokingly asked, “I’m going to the Louvre – do you need anything?” In spite of this, Picasso was soon found innocent, but Apollinaire wasn’t so lucky. When asked to vouch for him, Picasso would do nothing to help his best friend, probably because he (like Apollinaire) was a foreigner who wanted to stay out of trouble so as not to be thrown out of the country.

Two years after the robbery, the head of Florence’s Uffizi Museum received a strange message. A man claimed he had the actual Mona Lisa, and had been hiding it in a trunk since he’d stolen it from the Louvre. No one is exactly sure why the man chose to turn himself, and the painting, in. Some say he was trying to sell it to art dealers and experts in the area. Most agree that he was in league with South American conman Eduardo de Valfierno, who planned to sell forgeries of the missing painting, and had had some communication problems with the thief. Tests of the painting’s craqueleur (the pattern of small cracks that develops over time on an oil painting – a sort of fingerprint for an artwork) matched those that had been photographed from the real Mona Lisa years before it had gone missing. This Mona Lisa was the real one. The man who’d stolen it was named Vincenzo Peruggia. An Italian carpenter, he’d worked in the Louvre making picture frames. He claimed he stole the Mona Lisa because he wanted to bring it back to Italy, the country it had been robbed from. Unfortunately, it turns out he didn’t have his facts right. Though much of the Louvre’s collection is indeed the result of the spoils of war, the Mona Lisa had actually been purchased by French king François I from Da Vinci himself, after Da Vinci had stayed at the royal residence at Amboise for a number of years.

Peruggia was put on trial, and defended himself with wit and eloquence. He was jailed for one year, but this didn’t seem like too hard a sentence, since hundreds of women had fallen in love with him, and sent him cakes and care packages. Though what he’d done may not have been the best thing in the world, Peruggia had also made a point. The Mona Lisa was allowed to tour through Italy so that the Italian people could see this masterpiece created by their countryman more than three centuries before. Then, it was at last returned to the Louvre, where security had greatly improved.

But Mona’s adventures still weren’t over. In 1956, her existence was jeopardized again, when someone threw acid at her, damaging a lower portion of her canvass. A few months later, someone else threw a rock at her, chipping a few fragments of paint close to her left elbow. Luckily, she survived these mishaps and was restored. A few years later, from December 1962, through March 1963, she even left the Louvre for a time, to go to Washington DC and New York. In 1974 she visited Moscow and Tokyo.

Today, back in the Louvre, in a new space that was recently created for her, and in a new enclosure donated by the government of Japan, she is hopefully safely on view to anyone who wants to try to discover her mysteries…if they can make it through the crowds.