For centuries, people of all faiths have come to Rome and the Sistine Chapel to stare up at its immense ceiling and see Michelangelo's stunning masterpiece. To most, it is a beautiful vision from the Old Testament, frescoes painted on wet plaster of the stories of the creation of the universe, Noah's ark and Adam and Eve.
Dr. Arnold Nesselrath, the curator of the Vatican Museums, says people flock to the Sistine Chapel because "it's one of the greatest works of mankind that were ever produced and it's one of the greatest treasures of art."
But there are those who look at the 500-year-old frescoes — and see hidden messages.
"This, here, has so many layers of meaning upon meaning, and most of it, if not all of it, is from the Jewish tradition," says Roy Doliner, a Vatican tour guide. He and Rabbi Benjamin Blech, Associate Professor of Talmud, Yeshiva University, have written a book, "The Sistine Secrets: Michelangelo's Forbidden Messages in the Heart of the Vatican."
They say that Michelangelo embedded powerful and dangerous messages in the frescoes of the Sistine Chapel, that he encoded these messages using his knowledge of ancient Jewish texts, and that he intended some images as insults to the Pope himself.
Rabbi Blech says there's a reason that all the figures on the ceiling are Jews, the ancestors of Christ and Christianity.
"By emphasizing only Old Testament figures in the entire ceiling … what he was trying to say was, why we have ignored our true roots?"
Of course, 16th century Italy was a time and place that was overwhelming Catholic. But the authors say that Michelangelo was pointedly nudging the church to be kinder to Jews. In Florence, where he was raised, the young Michelangelo grew up in the household of the great Renaissance leader Lorenzo de Medici. It was here, the authors believe, that the artist would have been exposed to Judaism and its teachings.
One of the books the Medicis studied was at the center of an ancient form of Jewish mysticism: Kabbalah, as trendy then as it is today.
According to Doliner and Blech, Kabbalah is the key to cracking the code of many of Michelangelo's hidden messages. But their first clue didn't come from a Jewish scholar. Rather, it came from a tourist from Indiana who looked up at the famous panel of The Creation at the figure of God.
"In the late 1970's, a surgeon went into the Sistine Chapel, took a look at this [fresco]. He said to himself, wait, this is Anatomy 101 … this is actually a cross-section of the brain, the right hand side of the brain," Blech said.
If you look at the shape that frames God, and the flowing fabric that falls down from it — do you actually see a spinal cord?
"Now, what's interesting is in Kabbalah we have different kinds of wisdom," said Doliner. "The right side of the human brain in Kabbalah means wisdom — chokhma." And God is appearing from the right side of the brain in that fresco.
How about the fresco of Adam, Eve and the serpent in the garden? Most depictions of the Garden of Eden show an apple tree, but not on the Sistine ceiling. As in an ancient Jewish tradition, the tree is a fig tree.
Blech finds it another hidden message. "I think this is one of these powerful proofs, that not only did Michelangelo know Jewish texts, but he felt it important to incorporate the ideas of these texts into some of these frescoes."
Vatican Curator Nesselrath dismisses the Kabbalah references. "Well, we have all to remember that this is the palace chapel, the main chapel of the Vatican palace, and whatever Michelangelo is painting here had to be discussed with the Pope and his advisors."
And about that Pope — the authors of "The Sistine Secrets" claim that Michelangelo was furious at Julius II, who commissioned the work. Michelangelo was a sculptor, not a painter, and was angry to put his sculpture career on hold to paint frescoes. They say that anger caused the artist to paint hidden references on the ceiling to the corruption of the papacy of his time.
"All these things upset Michelangelo very much. My own personal feeling is that Michelangelo had to get this off his chest," Blech explained.
Just how badly behaved were the Popes of the Renaissance?
"There isn't a Renaissance Pope that didn't father plenty of children, and Alexander the Sixth had children — but this was well known," noted Michelangelo scholar professor William Wallace says.
Monsignor Timothy Verdon of Florence concurs, but can't imagine that Michelangelo gave it any thought. "Italians always understood that these men were human. If in their youth there had been a mistress or two, if there were illegitimate children, this was not really all that surprising. If the Pope went out of his way to favor his nephews … it was considered good policy … It's a bit hard to think that Michelangelo could have been deeply concerned with great questions of church reform."
But the authors contend that there are insults hidden in plain sight — right above the place where the Papal throne would sit. They point out the fresco of the Prophet Zachariah, directly above the Pope's seat. They say it's actually a portrait of the Pope himself.
"This is actually Julius II," said Blech. "Behind him, are little 'putti,' little angels. And this perhaps is the key to understanding Michelangelo's courage, Michelangelo's true feelings about the Pope, and the fact that Michelangelo did not hesitate to present us with messages that might've been offensive."
He says one of the putti is doing the Renaissance equivalent of giving the Pope's portrait "the finger."
"There's no doubt about it," he says, "this little putti, this beautiful little angel, is giving the finger not to Zachariah, but to Pope Julius."
He says the ceiling is full of insults, and that the hand gesture is seen again in the fresco of the Cumaean Sibyl.
"It happens a second time … Twice, that's a statement."
On Friday May 2 at 8 p.m. ET, ABC News anchor Martin Bashir travels to Florence and Rome and talks to to renowned Michelangelo scholars and theologians to find out if the authors' remarkable claims are true.