The film is based solely on footage shot in Warsaw in 1939 by Julien Hequembourg Bryan. This American filmmaker and photographer documented life in Poland, the Soviet Union and Nazi Germany between 1935 and 1939. Following the outbreak of the Second World War, he arrived in Warsaw, where he shot a number of films documenting the city under siege, and is said to be the only foreign correspondent in the Polish capital at the time. Bryan also took the first colour photographs of wartime Warsaw.