Critical mass of cyclists in Copenhagen during WWII

This picture was taken during the German occupation of Denmark 1940-45.

It would be interesting to know more about the background to this photo. It only states

Cyclists at Nørrebrogade in Copenhagen (1940-45). (Flickr) More photos at Danish resistance archives

The mood looks sombre, no-one is smilling. But, the road is packed with cyclists going one direction down the road.

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• Copenhagen Cycling