The secrets of the Grail are connected, according to the novel and movie, to Leonardo Da Vinci's work because Leonardo was a member of the Priory of Sion and knew the secret of the Grail. The secret is revealed in The Last Supper, in which no actual chalice is present at the table. The figure seated next to Christ is not a man but a woman, his wife Mary Magdalene. Most reproductions of the work are from a later alteration that obscured her obvious female characteristics.  

Leonardo da Vinci was already a well known artist when he created his masterpiece The Last Supper. He painted it on the back wall of the dining hall at the Dominican convent of Sta Maria delle Grazie in Italy . The reason the painting is laid out the way it is is that Leonardo was trying to "extend the room", to make it look like Jesus and his apostles were sitting at the end of the dining hall. This painting became an instant famous work, for many reasons.

The painting depicts the very moment that Jesus has said to his disciples:

Now when the even was come, he sat down with the twelve.
And as they did eat, he said, Verily I say unto you, that one of you shall betray me.
And they were exceeding sorrowful, and began every one of them to say unto him, Lord, is it I?
And he answered and said, He that dippeth his hand with me in the dish, the same shall betray me.
--Matthew 26

Dan Brown's error in The Da Vinci Code is that he calls the Last Supper a FRESCO. This painting is not a fresco. This is a critical mistake because if the painting had been a fresco, we would still have a superb image to view and examine. It is because it is not a fresco that we have all these questions now about what the painting is showing us. In fact, a main reason why the Last Supper painting is so famous is because it is not a fresco.

The painting took him four years to complete - 1495 to 1498. His patrons were furious at the delay but Leonardo refused to go any more quickly. Unfortunately, Leonardo's style experiment was a disaster. The paint almost immediately began falling off the plaster. The humidity was causing the paint to separate from the plaster on which it had been painted. Whole pieces of paint fell off the wall. Over the years, the piece has been vandalized and nearly fell apart completely.

Leonardo da Vinci was working based on the few known documents which describe this meal. As all artists do, he was trying to convey an impression and message, and took "artistic license" with his source material. Just as artists will often rearrange a scene in order to better convey what they are trying to have the viewer feel and think about, so did Leonardo da Vinci rearrange what was said about this important event, in order to convey his own thoughts and feelings on the subject.

Part of why Leonardo's version was so famous immediately was that he had chosen a very unusual way to portray the scene. Pretty much every painting of the Last Supper up until now had involved Jesus blessing the bread and wine - a nice, serene scene. Judas was always shown off in a corner, sulking, away from the rest of the disciples. This is what the Dominicans thought they were getting. When they instead got this "violent" version with the disciples all screaming and yelling, the monks were not exactly pleased. It created a lot of publicity.

Some people are intrigued by the three "lunettes" over the painting, not seen in most copies of the painting's image. These are tributes to Leonardo's patron duke. They are in fact the Sforza coat of arms. Leonardo's patron duke was Duke Lodovico Sforza So the center spot is the arms of the Duke plus his wife Beatrice d'Este. To the left is that of Massimiliano, the first born son. On the right side is Francesco, the second son.