The West was first alerted to the existence of this hidden treasure in 1991, when two Russian art historians, Konstantin Akinsha and Grigorii Kozlov, published an article in the American magazine Artnews (their attempts to get the story printed in Russia had failed). The two 34-year-olds have been beavering away ever since in Russian and German archives, in an attempt to piece together a full account of Stalin's art rape. The result is a book called Stolen Treasure which provides an extraordinary insight into the confusion, corruption and terror that surrounded the operation.
The Russian authorities are not amused by the young men's revelations. When the Artnews article came out, it caused a sensation. Isvestia, the major Russian daily newspaper, picked up the story from the New York Times, and Kozlov, who was still working for the Pushkin Museum, was summoned to the office of the director. After a diatribe, he offered to resign but his resignation was not accepted. "The director suggested that much more serious state punishment was in the pipeline," Akinsha told me, "but the publicity it would have generated in the West held them back."
For the past 18 months both men have lived in Germany, where Bremen University has given them a two-year study grant. German archives have been enthusiastically opened in the hope that their further researches will put pressure on the Russian government to return the treasures. So far, the outlook is not encouraging. A draft law currently before the Russian parliament would convert all the German treasures remaining on Russian soil into state property. The Russians take the view that the art was removed in compensation for treasures looted or destroyed by Hitler. They will not hand it back lightly.
The Russian art establishment broadly supports the draft law. "I support the basic principle," says Dr Mikhail Piotrovsky, director of the Hermitage Museum in St Petersburg. "At present, the art works stored in the Herm- itage and other museums are in limbo. If parliament establishes that they belong to the state, there will be a basis for negotiations with former owners."
Akinsha and Kozlov stress that art formed only a tiny part of the goods removed from Germany as war reparation. At the Yalta Conference in February 1945, Stalin demanded $10bn compensation for the damage his country had suffered during the Nazi invasion, and received the lukewarm agreement of his allies. He set up a secret "special committee on Germany" which was to be responsible for confiscating valuables in the occupied territories. "Entire factories were dismantled and transported from Thuringia, Saxony and Branden-burg to the Urals and Siberia. Millions of dresses, coats, men's suits and even hats were sent to Moscow, Leningrad and Kiev," the authors write in their book.
Planning for the removal of art works had begun back in 1943. Igor Grabar, one of the most feted Socialist Realist painters and a revered art historian to boot, had suggested that Soviet museums damaged by the Nazis should receive compensation in the form of equivalent art works from enemy collections. The government put him and a group of experts in charge of compiling lists of equivalents.
They got into some hilarious muddles over valuing art. One expert suggested calculating "the quantity of socially useful time for re- creation of a similar piece". To this, Grabar replied: "Do you think it is possible to re-create a painting by Rembrandt?" But Grabar had some far-fetched ideas of his own. For instance: "The easiest way to make restitution for the Church of the Saviour at Nereditsa is to take and import something like Rheims Cathedral." A vast Museum of World Art was planned, attached to the Pushkin Museum in Moscow.
The art that finally reached Russia bore little resemblance to these theoretical lists. What was taken depended on what was found in the territory the Russian army fought through.
After Stalin had established his special committee for Germany, all the ministries were required to send out brigades of "trophy" hunters to select suitable goods and ship them home. The Ministry of Culture's trophy brigades included theatre directors, art historians and musicians.
The Berlin brigade was directed by Andrei Belokopitov, former manager of the Moscow Art Theatre, a popular figure with the army's top brass, whom he had supplied with theatre tickets before the war. This stood him in good stead in a crazy argument over the carved frieze of the massive Zeus altar from Pergamum (now Bergama) in eastern Turkey - one of the ultimate masterpieces of Hellenistic art, excavated under the auspices of the Berlin Museum in 1878. It had been stored - along with the gold Schliemann discovered on the site of Troy in 1873 and presented to the German nation in 1881- in an anti-aircraft tower, or Flakturm, in the Berlin zoological garden.
The tower was taken over on 1 May 1945 by SMERSH, the Russians' military counter- intelligence service; they wouldn't let Belok-opitov in. Eventually, to get the Zeus altar out of the tower, he had to discard his uniform and approach Marshal Zhukov, the Russian commander in Berlin, on the basis of their pre-war theatrical acquaintance - it was the only way he could gain access. Zhukov faced up to SMERSH and had the altar out of the tower in 48 hours; it was removed by crane after a hole had been blown in the side of the building.
Despite this patriotic achievement, Belo-kopitov and Zhukov both ended up in disgrace. Belokopitov was accused of smuggling goods for his personal use on the plane that brought Schliemann's gold to Moscow, while Zhukov was found to have secreted fabulous riches of trophy art in his dacha and Moscow home. The investigating officer reported: "Zhukov's dacha is like an antique shop or museum, decorated with various valuable paintings, and there are so many of them that four paintings are hung in the kitchen. It is shocking to say, but in Zhukov's bedroom a huge painting depicting two naked women is situated over his bed! Among the paintings there are really valuable canvases that should ... be given to state foundations and placed in a museum." Zhukov was exiled to the Urals.
The official wholesale removal of art was accompanied by plenty of personal looting, but arrests were mainly limited to those who fell from political favour. Zhukov got off fairly lightly; others were tortured and executed.
The authors describe scenes of extreme confusion, with the contents of museums sent off by train, often inadequately packed and without documentation. In the case of the Dresden Gallery, urgent orders to search for a group of missing pictures were sent out without anyone realising that the paintings had already arrived in Moscow. This famous collection, which contained Raphael's Sistine Madonna, had been split up between various storage places and sent back to Russia by different organisations. The most important masterpieces were found in a mine in Gross Cotta - near Pirna, close to the Czech border - in circumstances that will never be completely understood. All the participants tried to claim the credit and published different accounts of what happened.
The pictures from Dresden were the first art works to be returned to East Germany. They were sent back amid loud fanfare in 1955. There was a second huge handover three years later. Special exhibitions were organised at the Pushkin Museum in Moscow and at the Hermitage in Leningrad before they left. After that, nobody mentioned that any trophy art was left in Russian museums - until Akinsha and Koslov blew the gaff in 1991.
! 'Stolen Treasure', by Konstantin Akinsha and Grigorii Kozlov, is published next week by Weidenfeld and Nicholson at pounds 20.