'The Black Flag' may refer to the German bombing of the small Spanish town of Guernica in April 1937 during the Spanish Civil War. Magritte later wrote that the picture 'gave a foretaste of the terror which would come from flying machines, and I am not proud of it.' In contrast to artists who praised technology, Magritte was showing that machines have their darker side. Looking closely at the planes, one can see that they are made of a variety of strange shapes. The plane on the bottom right has a long, curtained window where its wings should be.