From 1933 to the wars end, Nazi Germany systematically looted millions of works of art from individuals and the nations they went on to conquer.
The largest act of mass theft in history. But at the end of the war, with Nazi Germany in ruins, expert teams from the Red Army seized more than two and a half million art objects, some 12 million books and miles of archives.
Among them some of the great works of European art. Work beyond value. For Stalin these were reparations for the terrible damage and loss of life inflicted by the Nazi's on the Soviet Union.
Trophies of war but the Red Army, in its haste to seize so much, also brought back many thousands of works of art belonging to the victims of Nazism.
All of it was locked away in absolute secrecy for 50 years, until two Soviet researchers revealed all.
The international fall out continues to reverberate around the world. Germany and Russia continue to argue over the fate of these treasures and those victims of Nazism able to identify their works want them back.
And now, finally, the world has been able to see stunning works of Impressionism, ancient Trojan treasures and other works that have returned like ghosts from the past.
But are these the last prisoners of war? Charles Wheeler, in the company of Anne Webber from the Commission for Looted Art, investigates their fate in Looted Art.