The Last Supper
Leonardo da Vinci was already a well known artist when he created his masterpiece The Last Supper. He painted The Last Supper on the back wall of the dining hall at the Dominican convent of Sta Maria delle Grazie in Italy. The reason this 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 Last Supper 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.
In this painting the disciples are all reacting in horror to the thought that someone at that table would betray their master.
Fresco vs Tempera
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 - and therefore that it was in essence destroyed immediately after being painted. It's important therefore to understand this issue.
Normally, the way a painting like this would have been done would be a "fresco". That means that the plaster is made wet, and then the painting is done on the wet plaster. When the plaster dries, the paint is sort of intermingled with the plaster and it's nice and permanent. However, that type of painting is limited in its colors and can't be retouched. When the plaster dries, you're stuck.
Leonardo wanted to experiment with a new style he had invented - tempera (egg yolk and vinegar) plus oil painting on dry plaster. That way he could use more colors and redo portions if necessary. 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 on The Last Supper 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.
A recent twenty year effort tried to stabilize the piece for future viewing. Art experts tried to re-create what they thought the painting must have looked like originally. There is a lot of debate about whether those experts really did "fix" the painting, or if they changed its meaning by making changes in color and detail. There's no way to know, really, since The Last Supper had fallen apart so much over the years. Much of what we know about the way this painting was done and the fact that it was not a fresco was learned during that repair process.
I agree that some websites still claim the painting is a fresco. They are mistaken. You can't trust everything you read on the web :)
The Scene and Design
Leonardo da Vinci was working to create his version of The Last Supper 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.
I list several of Leonardo's changes below.
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. Remember, this was going to be at the end of their dining hall, where they would eat and relax!
When the Dominicans instead got this "violent" version with the disciples all screaming and yelling, the monks were not exactly pleased. The chaos that ensued 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 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.
Some versions of the painting have Latin words beneath it -
26:21 et edentibus illis dixit amen dico vobis quia unus vestrum me traditurus est
King James Version
26:21 And as they did eat, he said, Verily I say unto you, that one of you shall betray me.
So it is simply quoting the passage of the Bible that Leonardo was depicting. Again Leonardo chose to focus on the betrayal part of the scene, not on the quiet all-together-eating-a-meal part.
If you're curious, the top version of the Last Supper shown on this page was the pre-restoration version, while the second version is the one after restoration.
I have found a site with a High Resolution Image of the Last Supper - take a look!