Ingres' Grande Odalisque is one of, if not the most important paintings in art history.
It hangs in a gallery at the Louvre museum. If you haven't had the chance of going there, know that it is a huge sunlit room which itself is only a section of one of the most frequented corridors of the museum. On the side walls hang huge, famous, beautiful paintings by the likes of David, Delacroix or Géricault. Even though I'd already read about it, I had never seen the Odalisque other than thumbnails on glossy paper. I was admiring those gigantic paintings, and recounting to a friend the true story behind Liberty Leading the People and why it spent King Louis-Philippe's reign hidden in the Louvre's basement (let's just say it's no coincidence that it now hangs next to the Raft of the Medusa).
After about fifteen minutes admiring each painting I prepared to walk out, and on the wall that separated this room from the next, between doorways. It was so absurd that this painting should hang at the end of a room between doorways that I laughed out loud. I explained to my friend that this was what I loved about the Louvre. Wander 'round, find a masterpiece in a corner with people walking by it. The painting is beautiful. The odalisque's skin tone and curves give her an ethereal, oriental beauty. I never tire looking at it.
"But why is the painting so important?" you ask. Maybe you are fed up with this GTKY tripe about my museum wanderings, and I understand. Try this experiment. Fetch a picture of the painting on the Internet, and try to match the odalisque's position. You don't have to be naked. Can you match the odalisque's back's curve? Try hard. No? No matter how hard you try you won't be able to end up in the same position because, as Lometa pointed out, the odalisque has three extra vertebrae. Her right breast has been moved too, so it ends up in that space between her chest and her arm. It was no mistake on Ingres' part, all painters have to know their anatomy: he didn't just draw a longer back, he added three vertebrae under her flesh, and painted her.
What this means is that he painted something voluntarily unrealistic because it looked better. For the first time an artist put his aesthetic goal before realistic representation, he built his own reality for his work. This is what the impressionists would do, this is what opened the way for Monet and Picasso. Most people and even art history scholars overlook it, but there is truly a before and after La Grande Odalisque. And it's not just painting either: Ingres understood the great principle of all art, which is that it should never try to imitate the world outside, but rather the artist's own world. You're not looking at a window into the world, you're looking at it through the artist's eyes. Borrowing his soul.
TheLady points out that the Odalisque wasn't the first time a voluntarily unrealistic piece was made. Of course not, all 'primitive' art, and Medieval art didn't try to be realistic, but it remains that the dogma of Western post-quattrocento art was realism. Artists have always used things like composition and style to convey ideas, thank God, but Ingres was the first to be boldly unrealistic, and to break with that overwhelming tradition.