It’s one thing to steal a piece of artwork. But how does one steal an entire room?

Ask the Nazis, or maybe the Red Army. Either way, the Amber Room — a glimmering, opulent Soviet chamber sometimes referred to as the Eighth Wonder of the World — suddenly disappeared at the tail end of World War II. And it hasn’t been seen since.

The Amber Room was first conceived at the turn of the eighteenth century as part of the Charlottenburg Palace in Berlin, which was then part of Prussia and home to the Prussian royal family. Andreas Schlüter, the royal court’s chief architect, got the idea when he came across dozens of chests full of rare and extremely expensive amber nuggets in the palace’s cellar, and from there assembled an international team of artisans to help him complete the task. It wasn’t an easy one: Amber is notoriously finicky to work with, and covering an entire chamber in the stuff would require hundreds of thousands of small pieces, carefully heated, shaped, and joined together with acacia gum. Eventually, the team pulled it off, and the resultant room was not just a work of art in its own right, with a glimmer said to resemble stained glass, but also became an international sensation.

Among the Amber Room’s fans was Russian Czar Peter the Great, who visited Berlin in 1716 and expressed his admiration for the glowing chamber. By this time there was a new Prussian king on the throne, Frederick William I, who was looking to shore up his country’s alliance with Russia, and at the same time offload some of his late father’s less interesting treasures. Incredibly, this included the Amber Room. So King Frederick William offered the whole thing to Peter as a gift, and he gratefully accepted.

It took 18 crates to ship the massive jewel-encrusted panels to St. Petersburg, where the Amber Room was reinstalled in the czar’s Winter House. Later, in 1755, Czarina Elizabeth changed her mind and had the whole thing moved a few miles to the town of Pushkin. Once a series of renovations and alterations were complete, the revitalized Amber Room contained six tons of amber spanning 180 square feet. In all, the room was valued at the equivalent of $142 million dollars today.

And then it disappeared.

What happened? Well, the Nazis, for one thing. In June 1941, as Hitler’s troops suddenly marched into the Soviet Union, the order went out nationwide to remove and protect all major works of art from the invaders. But there simply wasn’t time for something as large and cumbersome as the Amber Room. So it was decided to instead simply cover it up with decoy layers of plain cotton and padding, to make it look like any other room. No such luck: Within hours, a pair of Nazi soldiers uncovered the glowing panels, and the whole thing was shipped back west to a castle in Königsberg.

Then, in August 1944, the castle and the city were heavily bombed by the Allies, and the fate of the Amber Room has been a mystery ever since. The simplest theory, obviously, is that the Amber Room was destroyed in the raids. But no remains were ever found, and besides, what fun is that? Instead, let’s consult some of the wilder theories that have surfaced since.

Some believe the room was secretly loaded onto a German military ship, which was later sunk in the Baltic. Others think the panels were broken up and quietly sold by the looting soldiers — a theory supported by a couple of smaller pieces reemerging in Germany in the 1990s. Over the years, several people have grabbed headlines by swearing that the Amber Room is hidden inside this mine, or at the bottom of that lake; none of these claims has ever borne out.

In their 2004 book The Amber Room, Catherine Scott-Clark and Adrian Levy uncover government reports suggesting that it was actually the Red Army itself that destroyed the Amber Room, by accident, along with the rest of Königsberg Castle, as they recaptured the city in April 1945 — and that the Russian government has kept this fact secret ever since, presumably for fear of the international embarrassment it would cause.

The Russians, for what it’s worth, deny all of this. They’d much rather direct your attention to the reconstructed Amber Room that recently opened in St. Petersburg’s Pushkin district in 2003, after a 25-year building process. The sequel cost approximately $11 million, and yes, if you’re wondering, President Putin attended the dedication.

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