Throughout six centuries,  the Ghent Altarpiece has been burned, forged,  and raided in three different wars. It is, in fact, the world’s  most stolen artwork. And while it’s told some of its secrets, it’s kept others hidden. In 1934, the police of Ghent, Belgium heard that one of the Altarpiece’s panels, split between its front and back, was suddenly gone. The commissioner investigated the scene but determined that a theft  at a cheese shop was more pressing. Twelve ransom notes appeared  over the following months and one half of the panel was even returned as a show of good faith. Meanwhile, art restorer Jef van der Veken made a replica of the other half  for display until it was found. But it never was. Some suspected that he was involved  in the theft and, once ransom demands failed, had simply painted over the original and presented it as his copy. But a definitive answer wouldn’t come for decades. Just six years later, Hitler was planning a grand museum, but was missing his most desired possession: the Ghent Altarpiece. As Nazi forces advanced, Belgian leaders sent the painting to France. But the Nazis commandeered and moved it to a salt mine converted into a stolen art warehouse that contained over 6,000 masterpieces. Near the war’s end in 1945, a Nazi official decided he’d rather blow up the mine before letting it fall into Allied hands. In fact, the Allies had soldiers  called Monuments Men who were tasked with protecting cultural treasures. Two of them were stationed 570 kilometers away when one got a toothache. They visited a local dentist, who mentioned that his son-in-law  also loved art and took them to meet him. They discovered that he was actually one of the Nazi’s former art advisors, now in hiding. And miraculously, he told them everything. The Monuments Men devised a plan to rescue the art and the local Resistance delayed  the mine’s destruction until they arrived. Inside, they found the Altarpiece among other world treasures. The Ghent Altarpiece, also called "The Adoration of the Mystic Lamb" after its central subject, consists of 12 panels  depicting the Biblical story. It’s one of the most influential artworks ever made. When Jan van Eyck completed  it in Ghent in 1432, it was immediately deemed  the best painting in Europe. For millennia, artists used tempera paint consisting of ground pigment in egg yolk, which created vivid but opaque colors. The Altarpiece was the first to showcase the unique abilities of oil paint. They allowed van Eyck to capture light and movement in a way that had never been seen before. He did this using brushes sometimes as tiny as a single badger hair. And by depicting details  like Ghent landmarks, botanically identifiable flowers, and lifelike faces, the Altarpiece pioneered an artistic mode that would come to be known as Realism. Yet, conservation work completed in 2019 found that, for centuries, people had been viewing  a dramatically altered version. Due to dozens of restorations, as much as 70% of certain sections had been painted over. As conservators removed these layers of paint, varnish, and grime, they discovered vibrant colors and whole buildings that had long been invisible. Other details were more unsettling. The mystic lamb’s four ears  had long perplexed viewers. But the conservation team  revealed that the second pair was actually a pentimento— the ghost of underlying layers of paint that emerge as newer ones fade. Restorers had painted  over the original lamb with what they deemed  a more palatable version. They removed this overpainting and discovered the original to be shockingly humanoid. The conservators also finally determined whether van der Veken had simply returned the missing panel from 1934. He hadn’t. It was confirmed to be a copy,  meaning the original is still missing. But there was one final clue. A Ghent stockbroker, while on his deathbed a year after the theft, revealed an unsent ransom note. It reads: it “rests in a place where neither I,  nor anybody else, can take it away without arousing the attention of the public.” A Ghent detective remains assigned  to the case but, while there are new tips every year, it has yet to be found.