It's the size of a barn door, weighs more than an elephant, and is one of the most famous and coveted paintings in the world.
It's the Ghent Altarpiece -- also called Adoration of the Mystic Lamb, after a central panel showing hordes of pilgrims gathered to pay homage to the Lamb of God.
Other panels depict the Annunciation, Adam and Eve, the Virgin Mary, John the Baptist and a crowned Christ in detail so exacting that you can pick out individual hairs in a beard, or dirt on a pilgrim's foot.
Artist Jan van Eyck completed the Ghent Altarpiece around 1432. Author Noah Charney tells NPR's Guy Raz that it's arguably the single most important painting ever made.
"It's the first great oil painting -- it influenced oil painting for centuries to come," Charney says. "It's the first great panel painting of the Renaissance, a forerunner to artistic realism. The monumentality of it and the complexity of it fascinated people from the moment it was painted."
Charney's new book, Stealing the Mystic Lamb: the True Story of the World's Most Coveted Masterpiece, traces the painting through six centuries of war, theft and intrigue.
150 Years Of Peace
The altarpiece was painted for the cathedral of St. Bavo, in Ghent. And during the first century of its existence, nothing much happened.
Then, in 1566, all hell broke loose. Protestant militants broke down the cathedral doors with an improvised battering ram, intending to burn the altarpiece, which they considered to be an example of Catholic idolatry and excess. But alert Catholic guards had disassembled the enormous work and hidden it in the cathedral tower, where it survived unscathed.
Over the next few centuries, the Ghent Altarpiece was taken as booty in the Napoleonic Wars and then returned to Ghent. Parts of it were stolen by a vicar at St. Bavo and ended up, after several sales, in a Berlin museum.
When World War I broke out, a brave cathedral canon hid the painting away in a junkman's wagon for safety. It took the Treaty of Versailles to finally reunite all the panels in their original home.
The Ghent Altarpiece didn't stay safe for long. Thieves broke into the cathedral one night in 1934 and made off with the lower left panel.
"This is the enduring mystery that really is part of the popular cultural awareness of the people of Ghent still to this day," Charney says.
The theft has never been solved. Visitors to St. Bavo Cathedral today will see a copy of the missing panel, painted during World War II. The copy is so good that many people thought it might be the original, hidden in plain sight, though recent conservation work has disproved that theory.
Raiders Of The Mystic Lamb
Missing panel and all, the Ghent Altarpiece was stolen one last time during World War II, on the orders of Nazi Gen. Hermann Goering.
"This may sound very silly," says Charney, "but in fact, the Nazis and Hitler in particular were absolutely convinced that the occult and the supernatural was real," and the Ghent Altarpiece was thought to be a sort of mystical treasure map showing the location of relics of Christ's passion.
The altarpiece ended up hidden with thousands of other looted artworks in a converted salt mine in Austria. The local SS commander had wired the mine with dynamite, determined to destroy all the art as the Allies began closing in.
Charney says the Ghent Altarpiece was eventually saved through the heroism of salt miners who disabled the bombs, and the work of local Austrian resistance fighters and Allied "monuments men" whose job it was to hunt for stolen art.
"There was this race," Charney says, "with the Allies trying to get to the mine before the SS could blow it up, and it was very close to every one of those works being completely destroyed."
But the painting was saved, and you can see it today at the St. Bavo Cathedral in Ghent.
"Each time I see it, I notice something new," Charney says. "For instance, I think it may be the first work of the pre-modern period to show someone laughing."