Some Dutch political prisoners were send off to the Zuchthaus (prison) in Siegburg, Germany. This envelop, which includes the letter, was sent by Willem Hammer to his wife in Rotterdam. It was sent from Köln, March 26, 1944. Of course, both the envelope and the letter have passed the German censor.
What’s special here is that there is also an invoice for the internment which has to be paid. The invoice is of the ‘Deutsches Landesgericht’ in The Hague, but at that moment (August 18, 1944) there was an office in Nijmegen, on the eastern border with Germany. The date, August 18, is just a month before Nijmegen was liberated!