But why is it so famous and what makes it such a masterpiece?
1. It was the product of years of meticulous iteration. It was Leonardo da Vinci’s pièce de résistance – for 16 years he carried it with him and improved it, adding layer after layer. He was so fond of it that he never delivered it to the person who commissioned it.

2. It’s astonishingly lifelike – a direct result of Leonardo’s scientific observations. You can’t get close enough at the Louvre to fully appreciate it, but it’s like gazing at the real person in the flesh (Italian noblewoman Lisa del Giocondo). That’s partly due to Leonardo’s understanding of optics. He pioneered “sfumato”, a technique of blurring the edges of figures to mimic what the human eye sees (i.e. the blur in our peripheral vision).

3. The most famous effect rendered by this is her flickering smile. Look at her lips directly and she isn’t smiling; focus elsewhere and a smile appears in the periphery of your vision. Leonardo spent countless hours dissecting corpses and understood the movements of every tiny muscle in the face. In the corner of Lisa’s mouth is a slight downturn – so faint that unless you look directly at it, it disappears in the blurred edges of your vision. The sfumato at the corner of her mouth accentuates this perfectly.

4. Almost as famously, her steady gaze follows you around the room. She seems to look directly at you (or just over your right shoulder as was recently concluded), whether you’re right in front of her or off to the side. There are competing scientific explanations for this, one being that the light, shadow and perspective of a 2D image are fixed, so they don’t shift depending on the viewer’s angle.

5. The attention to detail is impeccable. One example is the pupil of her right eye being noticeably wider than her left. From his optical studies, Leonardo was among the first to know that pupils dilate and contract in response to changing light exposure. It’s possible he spotted a case anisocoria in his subject, a condition which occurs in 20% of people and causes the pupils of each eye to dilate separately.

6. Leonardo was fascinated by how light hits curved surfaces, and deployed a clever trick to make the contours of her cheeks glow in an ethereal way. He used incredibly thin layers of transparent color atop a thick, white undercoat. Light that reaches the undercoat reflects back through, interplaying with light striking the surface. As lighting in the room changes, or your viewing angle does, she glows differently – adding to her lifelike luminescence.

7. The symbolism is striking. A defining concept of Renaissance humanism was the relationship between the “microcosm of man” and the “macrocosm of Earth”. Leonardo embraced this in his art and encoded it into the Mona Lisa – the backdrop is a living, breathing entity that flows into her. The distant river winds its way into Lisa’s scarf, and the fabric of her dress cascades like a waterfall.

The Mona Lisa is therefore the culmination of Leonardo’s mastery of multiple disciplines over the course of his life. He was one of the most diversely-talented people to ever live, and this painting reflects his achievements as an artist, scientist and philosopher.

English historian Kenneth Clark summarized it best:

“His insatiable curiosity, his restless leaps from one subject to another, have been harmonized in a single work.”